Petri Dish

The Petri Dish summons a pet Slime when used, which deals no damage. It grants the Pet Slime buff that lasts until the player manually cancels it by pressing/X or X/Square on the buff's icon in the armor section of the inventory screen, uses the Petri Dish again, or the player dies.

It can be obtained from Gold Chests and as a drop from Shadow Slimes.