Mob Rebirth is a mod that makes it so when mobs die, there is a chance that it will be 'reborn'. What exactly this means is up to how you configure it.
You can set defaults for these, and for each mob, you can customize:
- Rebirth Chance
- Chance of extra mobs spawning
- How many extra mobs can spawn
- Whether they should be reborn from player kills
- Whether they should be reborn from non-player kills
- Chances to be reborn as different kinds of mobs
- Which biomes they can be reborn in
- Whether they should take damage from sunlight (useful when there's a high chance that the undead will be reborn or spawn extras)
- Whether rebirth will drop a spawn egg instead of spawning another mob
I recommend using Mod Menu to configure this on the client because that's where the Config GUI is, but it is not required.
Demo/Configuration Tutorial (Mob Rebirth 9 for 1.16.3):