Betsy's Egg

Type	Pet summon
Use time	20 (Very fast)
Tooltip	Summons Itsy Betsy; 'No fire sacrifices required!'
Rarity
Sell	5
Research	1 required
Buff	Itsy Betsy
Buff tooltip	Itsy Betsy is following you
Use

Desktop/Console/Mobile-Only Content: This information applies only to the Desktop, Console, and Mobile versions of Terraria.

Master Mode-Only Content: This information applies only to Master Mode and Master Mode worlds.

Betsy's Egg is a pet-summoning item that drops from Betsy in Master Mode with a 25*1/4 (25%) chance. It summons Itsy Betsy, which will follow the player around.

Trivia

Itsy Betsy is a reference to the popular nursery rhyme "Itsy Bitsy Spider". Itsy bitsy also means small, as the pet is a miniature version of Betsy.
The item's sprite resembles the Gato Egg and Dragon Egg dropped from the Dark Mage.
Itsy Betsy is also a pet found in Dungeon Defenders 2, the game that the Old One's Army is based on.