How to make passive mobs hostile in minecraft

It's not possible to make Bats Killers but you can do this thing for a map with Bat Killers:

Create a new entity with command block (you can find some tutorials on Google)
Make a Resource Pack where the texture of the Zombie is reversed with that of the Bat (or another monster, whatever)
Finally, you can just make sure that the Bats attack only in the dark so that the player does not see them

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