Guide:Old One's Army strategies

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This is a Guide page.
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    The Old One's Army event differs from others in that the invading enemies do not attempt to kill the player; instead, they focus on destroying the Eternia Crystal used to summon it.

    The invasion is separated into three Tiers depending on progression. It will start at Tier 1, and after a mechanical boss has been defeated Tier 2 can be fought. Then, after taking down Golem for the first time, Tier 3 is available.

    The objective is to protect the Eternia Crystal from the enemies until all waves have been defeated.

    Summoning Conditions

    In order to summon the event, the Player must place the Eternia Crystal StandEternia Crystal Stand in a roughly flat terrain: a maximum of three tiles of vertical deviation is allowed, any more and the Stand will not accept the Eternia CrystalEternia Crystal.

    The arena needs to be at least 61 tiles long on each side of the Eternia Crystal Stand, measured from the center of the Stand (a 123-tile clearing in total, with the Stand at the center tile). The enemy portals will spawn further away if given the space however, up to 120 tiles away from the center of the Stand on each side. The area also needs 10 tiles of clear vertical space.

    General strategies

    Arena

    An example of an Old One's Army arena.

    Before facing the event, making a completely flat arena works very well. If an enemy's path to the Eternia Crystal is blocked, it will phase through obstacles, so trying to stop their progress with blocks won't be very effective. Building the floor with Asphalt BlockAsphalt Blocks will greatly increase movement speed. Using Potions is always a good idea, while it is also good to place CampfireCampfires, Heart LanternHeart Lanterns, Honey BucketHoney, Heart StatueHeart Statues and Bast StatueBast Statues (Desktop, Console and Mobile versions) to survive for longer. When fighting Tier 2 and 3, building a ceiling above the Eternia Crystal will protect it from Kobold Gliders, since they explode on contact with blocks.

    Build a raised platform 20 blocks off the ground, halfway between the Eternia Crystal and the expected portal location. Placing Flameburst TowerFlameburst Towers on these platforms will allow them to target flying enemies more easily, which can reduce swarming of the Crystal in later waves.

    Placing a vertical wall behind the spawning points of the portals will allow you to effectively cover both sides of the arena with bouncing projectile weapons like the Water Bolt and Pulse Bow. It may also be a good idea to build houses for competent combat NPCs like the Princess or Pirate behind the portals, so they can help kill enemies without any danger to themselves.


    Sentries

    Using one of the Tavernkeep's Sentries is also highly recommended, as they will greatly help when dealing with the many enemies the player will encounter. There are four different types with three tiers: Rod, Cane, and Staff, with the last being the strongest.

    • BallistaBallistas have the highest damage, but also the slowest fire speed. They shoot bolts that can pierce through enemies. When wearing Squire's Great HelmSquire armor or Valhalla Knight's HelmValhalla Knight armor, the bolts will pierce more and the player will get the Ballista Panic!Ballista Panic! buff when hit, which will double their fire speed. In addition, the Valhalla Knight armor will increase the attack speed.
    • Lightning AuraLightning Auras are a circle of lightning centered on the base that damages enemies repeatedly as they walk through them. They have the lowest base damage, but their damage is unaffected by enemy Defense. When used while wearing Monk's Bushy Brow Bald CapMonk armor or Shinobi Infiltrator's HelmetShinobi Infiltrator armor, they will deal damage slightly faster and they will receive a set 16% (for Monk) or 25% (for Shinobi Infiltrator) critical strike chance. In addition, the Shinobi Infiltrator set will increase the area of effect.

    After the event is summoned, the player will obtain ten Etherian ManaEtherian Mana, enough to summon one Tavernkeep's Sentry. Two Mysterious Portals will appear on the opposite ends of the arena; this where the enemies will spawn. Enemies will drop Etherian Mana when killed, allowing a player to summon more sentries as the event goes on.

    It is easy to get overwhelmed when fighting the enemies coming from both sides, so the player should constantly move to the left and right of the Crystal in order to prevent the enemies from reaching it. They should also always be on the watch for Etherian Wyverns and Kobold Gliders, as they can quickly get to the Crystal and deal a lot of damage to it. The Tavernkeep's Sentries will deal with the weaker grounded enemies; however, they are not very effective against flying enemies.

    It isn't necessary to get every sentry for each tier. An effective strategy is to use a close-range sentry, like the Lightning Aura or Explosive Trap at the portals and a long-range sentry like the Ballista or Flameburst closer to the center.

    Tier 1

    Dark MageT1
    Dark Mage.gif
    Classic Mode.png Classic
    Expert Mode.png Expert
    Master Mode.png Master
    Statistics
    Type
    Boss
    Environment
    Old One's Army
    AI TypeDark Mage AI
    Damage40/80/120 (contact)
    80160240 (Dark Energy) [1]
    Max Life800/1600/2040
    Defense18
    KB Resist100%
    Immune toConfusedShimmering
    Drops
    Sounds
    Hurt
    Killed

    Tier 1 is the easiest, as it possesses the weakest enemies and lasts five waves. It can only be summoned after the Eater of Worlds/Brain of Cthulhu have been defeated, as then the Tavernkeep will spawn for the first time.

    The player will see five different enemies:

    • The Etherian GoblinEtherian Goblin is the basic enemy of the event as well as the most common. It doesn't possess high stats or a special attack, making them very easy to kill.
    • The Etherian Goblin BomberEtherian Goblin Bomber and Etherian Javelin ThrowerEtherian Javelin Thrower are stronger enemies with ranged attacks. They will start spawning on Waves 2 and 3 respectively.
    • Etherian WyvernEtherian Wyvern is a highly damaging enemy with the ability to fly. It will quickly fly towards the Crystal, and then it will dive towards it. It will start spawning on Wave 4.
    • The Dark MageDark Mage is the Boss of the tier, spawning on Wave 5. It will alternate between shooting magical energy at the player, summoning Old One's SkeletonOld One's Skeletons and healing all enemies around it. It needs to be killed in order to finish the event.

    Master Mode: Ballistas are not fast enough to kill the grounded mobs, but three Lightning Aura sentries at each entrance can kill them quickly enough. In this mode, Etherian Wyverns can destroy your crystal in just seconds, so placing a couple Ballista sentries on a platform about 20 blocks off the ground can help in killing them.

    Recommended gear

    The event can be summoned at any time after defeating Eater of Worlds/Brain of Cthulhu, and should be done soon after.

    Armor

    • Obsidian Outlaw HatObsidian Armor should be obtained before attempting the Old One's Army. It offers the highest boost to summon damage in pre-hardmode, which is the most important stat as your sentries will do the majority of your damage. Every class should use this, as the boosts from any other set of armor are not very important for this event.

    Weapons

    In addition to their normal weapons, all classes should also use two of the Tavernkeep's Sentries.

    For all classes
    • The Houndius ShootiusHoundius Shootius performs well as an extra sentry that doesn't require Etherian mana.
    • The Crimson RodCrimson Rod does very decent damage, and can be set up between waves for some free extra damage.
    For Melee users
    • The VolcanoVolcano is amazing at close range, and also does well at crowd control with the explosions.
    • If obtained, the TerragrimTerragrim can do great damage to all enemies despite its short reach.
    • The AmazonAmazon is a great weapon, but it's better suited for single targets.
    • The Ball O' HurtBall O' Hurt/The MeatballThe Meatball are great against crowds.
    For Ranged users
    • A Molten FuryMolten Fury with Jester's ArrowJester's Arrows will excel against crowds.
    • Molotov CocktailMolotov Cocktails are exceptionally good at clearing the crowds, but struggle a bit with the Wyverns and the Dark Mage compared to other weapons.
    • The Star CannonStar Cannon is insanely good for this event, but the ammo for it is extremely tedious to obtain in large quantities.
    • The SandgunSandgun with Ebonsand/Crimsand pierces an infinite number of times without any damage penalty. It can be obtained before defeating any boss. By placing Background objects across the entire arena to prevent sand from obstructing it, the weapon can steamroll the entire event, even without support from sentries.
    For Magic users
    • The Demon ScytheDemon Scythe excels against crowds.
    • The Gray ZapinatorGray Zapinator is also a great choice, provided you've been lucky enough to obtain it.
    • The Weather PainWeather Pain is a homing secondary weapon that is especially good at defeating Etherian Wyverns.
    For Summoners

    Accessories

    • Mobility accessories such as the Lightning BootsLightning Boots and Shield of CthulhuShield of Cthulhu are useful to traverse to both sides of the event.
    • The Shark Tooth NecklaceShark Tooth Necklace provides a solid damage upgrade to all weapons.
    • Melee players will want to use Feral ClawsFeral Claws for an attack speed boost. Summoners may also want to use it as it grants increased speed to all whips.
    • Magic CuffsMagic Cuffs are useful to quickly regain mana as a mage.
    • Worm ScarfWorm Scarf can reduce damage taken by 17%.
    • In Hardmode, the Ancient Horn (Basilisk) or Blessed Apple (Unicorn) allows quick movement and charging through enemies.
    • The Bone HelmBone Helm attacks automatically, pierces through several enemies and is good against Etherian Wyverns.

    Sentry Placement

    Depending on the sentry, different placements will be needed. With ballistas, 2 should be place behind each portal, to ensure the pierce is used, and the rest should be placed closer to the crystal. With lightning aura sentries, 2-4 should be placed in a line maximizing the aura's range in front of each portal, until most enemies die without any other sources of damage. Explosive traps should be placed in front of each portal in a line, and platforms can be placed above the crystal so they'll also hit the Wyverns, but the placement is difficult to get right. Flameburst sentries should be placed close to the crystal. These placement tips hold true for all future tiers.

    Tier 2

    OgreT2
    Ogre.gif
    Classic Mode.png Classic
    Expert Mode.png Expert
    Master Mode.png Master
    Statistics
    Type
    Boss
    Environment
    Old One's Army
    AI TypeAttacker AI
    Damage70/140/210 (contact)
    122245367 (club swing) [3]
    120160240 (Ogre's Stomp)
    80120180 (Ogre Spit) [4]
    Max Life5000/10000/12750
    Defense34
    KB Resist100%
    Immune toConfusedShimmering
    Drops
    Sounds
    Hurt
    Killed

    After a mechanical boss has been defeated, the second tier can be fought. It's helpful, although not necessary, to grind out Tier 1 before defeating a mechanical boss, so that a Tier 2 sentry and full set of Tavernkeep armor can be acquired. All classes should use the War TableWar Table from Tier 1, as it allows for another Queen Spider to be summoned.

    The player will find five new enemies, and the four basic ones from the previous tier will get significantly higher stats, which is reflected by their different designs.

    • KoboldKobolds are one of the new enemies found. When near the player or the Eternia Crystal, it will quickly dash towards them, exploding on contact. The explosion deals high splash damage.
      • In the later waves, the player will also find Kobold GliderKobold Gliders, a variant with much lower stats but the ability to fly like Etherian Wyverns.
    • DrakinDrakins have high health, defense, and knockback immunity, making them very hard to kill. They are very slow, however they will fire magical shots from a distance.
    • Wither BeastWither Beasts will surround themselves with an aura of crystals which will inflict the Withered ArmorWithered Armor debuff, halving defense of players inside of it. They also possess high health, and they can regenerate damage taken.
    • The OgreOgre is the boss of the tier. It possesses very high damage and health, and does three dangerous attacks. From a long range, the Ogre will hurl a ball of snot at a target, it will only damage targets it hits but it will inflict the OozedOozed debuff on any nearby player, slowing them down significantly. It can also jump into the air and land with a shockwave, doing area damage about ten blocks forward in each direction on the ground. At very close range, it will strike with its club, dealing very high damage. Like the Dark Mage, it needs to be the last enemy killed in order to finish the event. When killed it also drops a unique Accessory or Weapon.

    Recommended gear

    Armor

    • If available, any set of Tavernkeep armor is much better than any other set of armor.
    • Spider MaskSpider armor is the next best choice, offering decent defense and high summon damage boosts.
    • Forbidden MaskForbidden armor is great for mages, as the offensive boosts and tornado summon make it better than the Spider armor.

    Weapons

    Just like in Tier one, all classes should also use one of the Tavernkeep's Sentries with their normal weapons.

    For all classes
    • The Clinger StaffClinger Staff is the single most impactful non-summoner weapon due to its high knockback, which completely neutralizes most of the weaker enemies.
    • The Nimbus RodNimbus Rod can contribute a a solid bit of damage when placed just in front of the portals.
    • The Queen Spider StaffQueen Spider Staff is fantastic as an extra sentry that doesn't require Etherian mana.
    • The Crimson RodCrimson Rod does very little damage, but it can still be mildly helpful since it can be set up before the event.
    • The Spider StaffSpider Staff is the best summon weapon for non-summoners.
    For Melee users
    For Ranged users
    For Magic users
    • The Magical HarpMagical Harp is excellent against crowds. The Shadowflame Hex DollShadowflame Hex Doll is useful as well.
    • The Unholy TridentUnholy Trident is harder to get than the above two weapons but is more powerful against crowds.
    • The Life DrainLife Drain has no pierce cap and can kill large groups of weak enemies very quickly, it's also helpful to quickly heal up after taking damage.
    • The Meteor StaffMeteor Staff is great for all enemies, but consumes a large amount of mana.
    • The Sky FractureSky Fracture and Crystal SerpentCrystal Serpent are strong against single targets.
    • The Golden ShowerGolden Shower is a good secondary weapon with piercing capabilities.
    For Summoners
    • The Sanguine StaffSanguine Staff combined with the FirecrackerFirecracker is great against crowds, as the explosions will deal with a lot of enemies. Abigail's FlowerAbigail's Flower can be used as a much easier to obtain alternative to the Sanguine Staff.
    • The DurendalDurendal is the best whip available for other minions, and can be stacked with the Cool WhipCool Whip to great effect.
    • The Blade StaffBlade Staff performs quite well against this event, especially when combined with the above whips.
    • A Flask of IchorFlask of Ichor can be used to allow your whips to inflict the ichorichor debuff.

    Accessories

    • Angel WingsWings are extremely useful in hardmode.
    • Mobility accessories such as the Shield of CthulhuShield of Cthulhu or the Frog LegFrog Leg and any of its upgrades are very useful as well.
    • A matching class Emblem should be used, a Summoner EmblemSummoner Emblem can also be a helpful filler accessory for non-summoners.
    • A Berserker's GloveBerserker's Glove can be very helpful for both melee users and summoners.
    • A Moon StoneMoon Stone provides solid all-round stat boosts for all classes.
    • Variants of the Magic QuiverMagic Quiver make for good filler accessories for rangers.
    • Mages should use variants of the Celestial MagnetCelestial Magnet, since collecting mana stars from far away will be helpful.
    • Summoners should use the Squire's ShieldSquire's Shield/Apprentice's ScarfApprentice's Scarf, they offer solid damage boosts and allow for another Queen Spider to be summoned.
    • The Pygmy NecklacePygmy Necklace is also great for summoners, as it allows for another minion.
    • Variants of the Cobalt ShieldCobalt Shield and Cross NecklaceCross Necklace can help when taking damage.
    • Magic CuffsMagic Cuffs are good for regaining Mana. They can be used as a source of infinite mana by standing on Spikes.
    • Volatile GelatinVolatile Gelatin is effective against grounded enemies that get close to you.

    Tier 3

    BetsyHardmode exclusive
    Betsy.gif
    Map Icon Betsy.png
    Map Icon
    Classic Mode.png Classic
    Expert Mode.png Expert
    Master Mode.png Master
    Statistics
    Type
    Boss
    Environment
    Old One's Army
    AI TypeBetsy AI
    Damage80/104/156 (contact)
    70140210 (Betsy's Fireball)
    70140210 (Betsy's Breath) [6]
    Max Life50000/75000/95625
    Defense38
    KB Resist100%
    Immune toOn Fire!ConfusedHellfireShimmering
    Inflicts debuff
    Inflicts debuff
    Inflicts debuff
    DebuffOn Fire!On Fire!
    Debuff tooltipSlowly losing life
    Chance100% (Betsy's Breath)
    Duration7–10 seconds14–20 seconds17.5-25 seconds [7]
    Drops
    Projectiles created
    Projectiles created
    Projectiles created
    • Betsy's Fireball
      Betsy's Fireball
    • Betsy's Breath
      Betsy's Breath
    Sounds
    Hurt
    Killed
    Charge
    Betsy's Fireball
    Betsy's Fireball impact
    Betsy's Breath
    Flying Circle
    Roar
    Summon
    Etherian Wyvern

    After the Golem has been defeated, the third and final tier of the Old One's Army can be fought. Again, grinding out Tier 2 before defeating Golem is beneficial, but not required. All classes should use the War TableWar Table from Tier 1, as it allows for another Sentry to be summoned.

    Like the previous tiers, enemies will get significantly higher stats, and some will also get new designs. There are also two new ones:

    • Etherian Lightning BugEtherian Lightning Bugs will quickly fly near the Crystal, and attack it with energy projectiles. They will inflict Withered WeaponWithered Weapon on hit, which will temporarily halve the damage output of all weapons.
    • Betsy, who will spawn on Wave 7 serving as the final boss of the event. Unlike the other enemies, she will directly focus on killing the player instead of the Crystal. Her attacks consist of spinning in circles before charging multiple times, breathing fire, shooting fireballs and spawning Etherian Wyverns. While her attacks don't deal too much damage to the Crystal, the threat of the other enemies can make the final wave significantly harder than the others. Like with the Dark Mage and Ogre on Tiers 1 and 2, killing her will end the event.

    Gearing Up

    Armor

    • Any Tier 3 set of armor are the best sets available for the event by far, and most other armor should be disregarded.
    • The next best armors available are the Monk's Bushy Brow Bald Cap.pngSquire's Great Helm.pngHuntress's Wig.pngApprentice's Hat.png tier 2 armors sold by the Tavernkeep. While they have worse stats than post-Golem armors, most of the damage done during this event is from the sentries themselves. Thus, using armor that boosts sentry damage will results in far higher DPS than damage from player weapons.
      • The exception to this is Apprentice armor, whose set bonus does not directly benefit the DPS of Flameburst towers. The hat should be replaced with a Forbidden MaskForbidden Mask if available.
    • Spooky HelmetSpooky armor can outclass the Tier 3 armor on a pure summoner build.


    Weapons

    For all classes
    • The Clinger StaffClinger Staff remains incredibly useful for destroying all enemies that are susceptible to knockback.
    • The Nimbus RodNimbus Rod can contribute some DPS over the entire event.
    • The Rainbow GunRainbow Gun shreds entire waves of enemies and can be used as a last resort to defend the Eternia Crystal. Note that it has a lower duration than the Clinger Staff and Nimbus Rod, and must be refreshed after every wave.
    • The Proximity Mine LauncherProximity Mine Launcher can be used between waves to heavily damage Ogres and other enemies that are resilient enough to get close to the Crystal. It can also be deployed near the Crystal at the end of Wave 6 to significantly chunk Betsy's health.
    • The Staff of the Frost HydraStaff of the Frost Hydra can be used as an extra sentry that doesn't cost Etherian Mana. If using sentry-boosting equipment, several can be summoned.
    • The Crimson RodCrimson Rod provides an incredibly small amount of damage, but there is no reason not to set it up before the event for a little bit of extra damage.
    For Melee users
    • The Influx WaverInflux Waver and theSeedlerSeedler are the strongest swords available.
    • The The Horseman's BladeThe Horseman's Blade and the Terra BladeTerra Blade are effective against large groups of enemies.
    • The North PoleNorth Pole is a great spear for crowd control as its projectiles cover an very wide area. It is very effective on Wave 7, since it can handle Betsy and the enemies at once.
    • The Eye of CthulhuThe Eye of Cthulhu is the strongest yo-yo available.
    • The Scourge of the CorruptorScourge of the Corruptor and Vampire KnivesVampire Knives can beat the event, although their overall damage is lower than that of piercing weapons.
    • With the right setup, the Fetid BaghnakhsFetid Baghnakhs can deal an extreme amount of damage to all enemies and bosses.
    • Beginning players may have trouble seeing Betsy in all the confusion. Homing weapons can make this part of the fight easier. Some homing melee weapons available at this stage include (from weakest to strongest) Possessed Hatchet, Scourge of the Corruptor, Seedler, and Flairon. More experienced players are better off aiming a higher-DPS weapon directly at Betsy.
    For Ranged users
    For Magic users
    For Summoners
    • The Xeno StaffXeno Staff, TerraprismaTerraprisma, and Desert Tiger StaffDesert Tiger Staff are the best minions available.
    • The Dark HarvestDark Harvest makes your minions do additional damage to nearby enemies, letting the player focus on bosses while the dark energy kills smaller enemies.
    • The KaleidoscopeKaleidoscope provides the highest tag damage against bosses.
    • The Morning StarMorning Star offers the best raw damage against crowds, but has a relatively mediocre tag effect.
    Accessories

    It's recommended to reforge all accessories to Menacing to maximize damage dealt by sentries. Warding is less effective than usual, as the goal of this event is to defend the crystal and not oneself.

    Potions

    Specific strategies

    Boulder Drop

    An effective and easy to use strategy, especially pre-Hardmode. First, you must add a roof to your arena, about 15-25 blocks above the ground. Then, you must collect as much Stone as you think is necessary, which may take some time. You must then take a Heavy Work Bench to a Graveyard and craft as many Boulder Statues as possible. Bring the statues back to your arena, and place them along your newly constructed roof. You should get some wire, wrenches, and a timer, and a switch is recommended, all of which can be bought from the Mechanic. All you need to do now is connect the wires to the Boulder Traps and timer, and place two blocks on each side of the Eternia Crystal to prevent the boulders from damaging it or you, without being too high to start the event. You may also place some platforms above the boulders, so you can still move around without taking as much damage from them. Note that the boulders only fall every 15 seconds, which means you should leave enough space for the portals to spawn at maximum distance. You will also want the ground to be flat, so the boulders can go all the way across the arena. Using this tactic, you only need to defeat flying enemies, such as Etherian Wyverns or Lightning Bugs, along with any bosses that spawn. Note that this tactic works best in lower tiers, and only adds additional damage to enemies on higher ones.

    Actuator Drop

    Since the crystal stand can be actuated, the entire event crystal can be dropped down, much like the flat terrain the event requires. If the Eternia Crystal (NPC)Eternia Crystal (NPC)(Desktop, Console and Mobile versions) stands on sufficient ground for the various grounded enemies in the event to stand on, or on its initial elevation, they will float toward the crystal with a shadow aura and still reach it. However, if the crystal is dropped to a single platform or block, and grounded enemies are dropped beforehand (recommended roughly 40 blocks from the center), they'll only float if they get far enough down from the crystal, in which case they float diagonally toward the crystal. When employing this strategy, you should consider placing a water platform (using BubbleBubbles(Desktop, Console and Mobile versions)) and using some iteration of Water Walking BootsWater Walking Boots or a Water Walking PotionWater Walking Potion to provide yourself with a platform underneath the crystal, but also to cancel enemies floating toward the crystal: since water is considered a physical block, they'll stop floating. The by far most effective strategy, to solve the issue of floating, is on the other hand placing a long platform of blocks at least 65 blocks below the crystal entity's platform, with a 5 wide by 10 high chamber in the middle.

    A working actuator drop arena
    A full actuator drop arena. Note that what constitutes the non-actuated part of the center is all platforms, allowing for easy reach of the flying enemies. The crystal is dropped to the granite platform, slightly below the stand.

    If the Eternia Crystal (NPC)Eternia Crystal (NPC)(Desktop, Console and Mobile versions) is dropped down onto a single block, the enemies are dropped down 40 blocks away from the center and a platform 65 blocks down is built, with a 5 by 10 chamber, these are the results:

    • No ground based enemies, i. e. no Etherian GoblinEtherian Goblins(Desktop, Console and Mobile versions), Etherian Goblin BomberEtherian Goblin Bombers(Desktop, Console and Mobile versions), Etherian Javelin ThrowerEtherian Javelin Throwers(Desktop, Console and Mobile versions), KoboldKobolds(Desktop, Console and Mobile versions), DrakinDrakins(Desktop, Console and Mobile versions) or Wither BeastWither Beasts(Desktop, Console and Mobile versions) are able to be in range of or reach the crystal, and effectively deal no damage, with one exception, discussed below.
    • A Lightning AuraLightning Aura(Desktop, Console and Mobile versions) can be placed in the 5 by 10 chamber to provide consistent damage against all of the above. The tougher enemies (not Etherian GoblinEtherian Goblins(Desktop, Console and Mobile versions) or Etherian Goblin BomberEtherian Goblin Bombers(Desktop, Console and Mobile versions)) won't consistently spend time in the chamber (instead they'll skip out) but since they can't damage the crystal this is irrelevant to the progress of the event. Using higher level Lightning AuraLightning Auras(Desktop, Console and Mobile versions) provides faster progression, which is useful when you're trying to farm the event for Defender MedalDefender Medals(Desktop, Console and Mobile versions).
      • Note that this is a much better solution than only using summons, since only using summons can actually incite DrakinDrakins(Desktop, Console and Mobile versions) to float up toward the crystal. Using summons in conjunction with a Lightning AuraLightning Aura(Desktop, Console and Mobile versions) is effective.
      • An alternative is not to use Lightning AuraLightning Auras(Desktop, Console and Mobile versions) but instead rely on piercing weapons such as the Magical HarpMagical Harp. This strategy is extremely viable since the NPC limit of 200 is quickly reached when the player isn't actively killing the enemies, which means that the flying enemies attacking the portal will spawn predictably and in lower numbers. The number of enemies spawning from new waves will also be controllable.The main downside to this is that DrakinDrakins(Desktop, Console and Mobile versions) can follow you and float toward the crystal if inadequately dealt with when visiting the platform. Standing right below the crystal does temporarily disable their floating when they reach your position, but due to their high damage this can be extremely deadly, especially considering the high health of DrakinDrakins(Desktop, Console and Mobile versions).
    • The Dark MageDark Mage(Desktop, Console and Mobile versions) and OgreOgre(Desktop, Console and Mobile versions) are unable to damage the Eternia Crystal (NPC)Eternia Crystal (NPC)(Desktop, Console and Mobile versions). The 40 blocks in distance from the center are valuable since the Dark Mage will stop roughly that length away from the crystal and try to summon Old One's SkeletonOld One's Skeletons(Desktop, Console and Mobile versions), a spell which will fail since there is no ground for them to be summoned on. The Dark Mage is thereby unable to inflict any damage. Likewise, the 65 blocks down the platform was placed is specifically such that the Ogre's balls of snot won't hit a player defending the crystal slightly from below, or the crystal itself.
    • Effectively, the player can go the all three tiers worrying solely about Etherian WyvernEtherian Wyverns(Desktop, Console and Mobile versions), Kobold GliderKobold Gliders(Desktop, Console and Mobile versions) and Etherian Lightning BugEtherian Lightning Bugs(Desktop, Console and Mobile versions), as well as BetsyBetsy(Desktop, Console and Mobile versions). For enemies, placing Flameburst TowerFlameburst Towers(Desktop, Console and Mobile versions) is an effective way to provide damage and knockback high enough to keep the flying enemies away from the crystal, even more so with summoner gear. With effective placement and sufficient armor, the event becomes mostly automatic even in Master Mode, apart from BetsyBetsy(Desktop, Console and Mobile versions). It's always a good idea to keep an eye on the Eternia Crystal (NPC)Eternia Crystal (NPC)(Desktop, Console and Mobile versions) at all times, on the other hand, especially in earlier waves.

    Bootstrapping

    The higher tiers of the Old One's Army, especially in Master Mode, are incredibly difficult. This strategy, though, relies on the first tier being comparitively easy.

    The main idea here is that almost all damage is done by the sentries. So this strategy focuses on getting the best sentries and maximizing summon damage.

    1. Beat the first tier of the Old One's Army using one of the strategies on this page (an especially easy strategy is Jester Arrows for ground-based enemies and the Imp Staff for flying enemies).
    2. Repeat. Save up 15 Defender Medals. Saving up 30 will make things even easier.
    3. Craft a Queen Spider Staff. If possible, also find a Nimbus Rod and/or Clinger Staff
    4. Unlock tier 2 of the Old One's Army by defeating a mechanical boss. Immediately buy a Tier 2 sentry from the Tavernkeep, or two if you have saved up 30 defender medals.
    5. Defeat as many rounds of Tier 2 OOA as you can, using the Queen Spider Staff, Nimbus Rod, Clinger Staff, tier 2 sentries, and your best weapon. If you can't defeat Round 7, collect as many defender medals as you can and save up for one of the armor pieces sold by the Tavernkeep. The chest piece should generally be bought first, as it tends to have very good bonuses to both sentries and the class of your choice. Wearing the full set will allow you to place 3 Spider Queen Sentries, gives you bonuses comparable to Hallowed Armor in your favored class, boosts your sentry damage by 30%, and (for all classes except mages) boosts their preferred Sentries DPS significantly.
    6. Farm the Ogre for one of the +1 sentry accessories. Collect at least 60 defender medals, or 120 to be safer.
    7. Try to collect the rainbow gun (optional), Frost Hydra (optional) a Papyrus Scarab, and a Necromantic Scroll.
    8. Unlock Tier 3 of OOA by defeating Golem. Immediately purchase 1-2 tier 3 sentries.
    9. Wear your papyrus scarab, necromantic scroll, +1 sentry accessory, and any other damage-increasing accessories (such as Summoner Emblem or Celestial Shell, but not including critical hit accessories, as they don't affect summons). Wear the armor you received from the Tier 2 OOA, even if it's worse than your other armor; remember, you're trying to maximize sentry damage, not weapon damage.
    10. Farm rounds 1-6 for medals. Start replacing your tier 2 armor with tier 3 armor, one at a time.
    11. Once you have full tier 3 armor, you are ready to face Betsy. Make sure many of your sentries are in the middle of the map, since they will do most of the damage. When she attacks, your sentries should be powerful enough to kill all enemies approaching the crystal, especially if you use an AOE/homing weapon like Seedler, Flairon, Cluster Rocket I, Bat Scepter, etc. that can take out the Wyverns she occasionally summons.

    If you are unable or unwilling to farm for medals ahead of time for buying armor from the Tavernkeep, wearing Obsidian armor for tiers 1 and 2 and Spooky armor for tier 3 will give you similar benefits.

    Finally, since your build maximizes summon damage in this method, you might as well use the best minions available, such as the Sanguine Staff or Xeno Staff.

    Tips

    Do note that Etherian Lightning BugEtherian Lightning Bugs(Desktop, Console and Mobile versions) fly in line with the crystal's height rather than quite far above it like the other flying enemies, so anyone entering Tier 3 should be ready to place Flameburst TowerFlameburst Towers(Desktop, Console and Mobile versions) close to and in level with the crystal to ensure aid with the bugs.

    Additionally, make sure to bring a Treasure MagnetTreasure Magnet(Desktop, Console and Mobile versions) and a Rod of DiscordRod of Discord to be able to safely teleport under the platform and collect the Etherian ManaEtherian Mana(Desktop, Console and Mobile versions). Also, consider building the platform out of Conveyor BeltConveyor Belts(Desktop, Console and Mobile versions) to collect the mana in a more central location.

    Most importantly, to be able to view the Eternia Crystal (NPC)Eternia Crystal (NPC)(Desktop, Console and Mobile versions) while killing the OgreOgre(Desktop, Console and Mobile versions), collecting Etherian ManaEtherian Mana(Desktop, Console and Mobile versions), or personally killing the enemies in the box, bring BinocularsBinoculars, a Sniper RifleSniper Rifle or simply use any iteration of the Rifle ScopeRifle Scope to provide an increased range of view and some oversight of the crystal. Ranged builds are recommended for this strategy since they can utilize a scope for accessible good sight and high precision in killing the flying enemies. Use non-homing bullets.

    Consider placing banners for WyvernWyverns, HarpyHarpies and Angry NimbusAngry Nimbuses if the arena is placed relatively high above the surface, since they can spawn during the event and be a significant distraction, as well as deal damage. Especially WyvernWyverns.

    References

    1. ↑ Information taken from the Desktop version Desktop 1.4.0.5 source code, method AI_109_DarkMage() in Terraria.NPC.cs. There may be inaccuracies, as the current Desktop version Desktop version is 1.4.4.9.
    2. ↑ Information taken from the Desktop version Desktop 1.4.0.5 source code, method RegisterDD2EventDrops() in Terraria.GameContent.ItemDropRules.ItemDropDatabase.cs. There may be inaccuracies, as the current Desktop version Desktop version is 1.4.4.9.
    3. ↑ Information taken from the Desktop version Desktop 1.4.0.5 source code, method GetMeleeCollisionData() in Terraria.NPC.cs. There may be inaccuracies, as the current Desktop version Desktop version is 1.4.4.9.
    4. ↑ Information taken from the Desktop version Desktop 1.4.0.5 source code, method AI_107_ImprovedWalkers() in Terraria.NPC.cs. There may be inaccuracies, as the current Desktop version Desktop version is 1.4.4.9.
    5. ↑ Information taken from the Desktop version Desktop 1.4.0.5 source code, method RegisterDD2EventDrops() in Terraria.GameContent.ItemDropRules.ItemDropDatabase.cs. There may be inaccuracies, as the current Desktop version Desktop version is 1.4.4.9.
    6. ↑ Information taken from the Desktop version Desktop 1.4.4.9 source code, method AI_110_Betsy() in Terraria.NPC.cs.
    7. ↑ Information taken from the Desktop version Desktop 1.4.0.5 source code, method StatusPlayer() in Terraria.Projectile.cs. There may be inaccuracies, as the current Desktop version Desktop version is 1.4.4.9.
    8. ↑ Information taken from the Desktop version Desktop 1.4.0.5 source code, method RegisterBoss_Betsy() in Terraria.GameContent.ItemDropRules.ItemDropDatabase.cs. There may be inaccuracies, as the current Desktop version Desktop version is 1.4.4.9.
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