Mob Rebirth is a mod that makes it so when mobs die, there is a chance that it will be ‘reborn’. You can configure most features of the mod, including whether ‘rebirth’ means dropping the spawn egg(Not recommended) or spawning another of the same mob in its place, rebirth chance, whether animals can be reborn, whether mobs can die from anything or just being killed by the player, whether or not extra mobs should be reborn, the chance for extra mobs to be reborn, and the extra mob rebirth mode.
More Configurable features:
Should slimes be reborn?(Because of Mob Rebirth; I am not messing with vanilla slime spawning the littler ones)