Enemy specific drops.

I recently had the idea that enemies should have there own exclusive drops that appear very rarely when killing these mobs. These drops consist of pets, weapons, and artifacts.

For example:

Enchanter could drop a tome that buffs nearby allies and summons

Witch could drop a potion related item that, to all enemies that step in its radius, gives a random buff or debuff such as strength or poison

Vindicator Chef's could drop a chef hat cosmetic

Geomancer could drop his staff (idk if this would be an artifact or a weapon) that does similar things to what he does

Key Golem after unlocking a certain amount of doors with the specific key a pet for that specific key golem could be unlocked

Corrupted Cauldron could drop wither a conjured slime pet or an artifact that summons conjured slimes 

Nameless One could drop his staff

I also think it would be cool to get an Arch-Illager companion after completing the Apocalypse mode of the game