Tablet Fragment

Not to be confused with the Solar Tablet Fragment.

The Tablet Fragment is a pet item which has a 25% chance to drop from the Lunatic Cultist in Master mode. It summons a Phantasm Dragon pet that will follow the player around. It resembles the phantasm dragon spawned during the boss fight, aside from having fewer legs.

Trivia
The Tooltip ,,It keeps looking at the Moon" may be a reference to the Endboss off the Game, Moon Lord, and to several other moon-related things throughout the game.