Piece of Moon Squid

Type	Pet summon
Use time	20 (Very fast)
Tooltip	Summons a Moonling; 'The forbidden calamari.'
Rarity
Sell	5
Research	1 required
Buff	Moonling
Buff tooltip	A friend from beyond
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.

Not to be confused with the Suspicious Looking Tentacle.

The Piece of Moon Squid is a pet item that has a 25*1/4 (25%) chance to drop from the Moon Lord in Master Mode. It summons a pet Moonling that resembles the Moon Lord's head.

Trivia

The item's tooltip, "The forbidden calamari", is likely a reference to a common internet meme, where some form of object similar to a food, which in reality isn't edible, is nicknamed "Forbidden <food>", for example sea glass being referred to as "forbidden fruit snacks". Calamari is fried squid, referring to the Moon Lord's cephalopod appearance.
This pet bears a resemblance to Cyrax, an alien boss from the 2001 video game Insaniquarium.
This pet itself marginally resembles the Ancient Vision, an enemy summoned by the Lunatic Cultist if the player attacks a duplicate of the Lunatic Cultist while the Phantasm Dragon is still alive.
The buff tooltip, "A friend from beyond", is a reference to H.P. Lovecraft's short story "From Beyond", which is a story of a man who witnesses alien creatures in alternate dimensions. The Moon Lord, which the Piece of Moon Squid drops from, also happens to be a reference to H.P. Lovecraft – this time, the cosmic entity Cthulhu, a fictional character Lovecraft created.