I have an idea for a class, a mushroom that could have the name cordy, a reference to Ophiocordyceps that infects and mind controls insects.
That mushrooms ability would be, to empty a heart, or if the player has only temporary hearts, to spend one, to revive a killed enemy as a zombie to fight, kill, take damage and die for the player.
That former enemy would color swap the pallet, to avoid confusion and would not leave the player until either it, or the player dies.
Also, when reviving a boss enemy, the former enemy boss would shrink down, to regular enemy size.