The animals no longer despawn and their spawn is based on the biome seed. In other words, the randomness of spawning was removed. There are several mods that relied on the prior mob spawning method to add custom mobs to the game, like Mo’Creatures, More Creeps and Weirdos, Humans+ and many more.

Custom-Mob-Spawner-Mod

Requires:

Minecraft Forge

Custom Mob Spawner Mod Download Links:

Older versions:

For Minecraft 1.5.2

Download from Server 1Download from Server 2

For Minecraft 1.6.2

Download from Server 1Download from Server 2

For Minecraft 1.6.4

Download from Server 1Download from Server 2

For Minecraft 1.7.2

Download from Server 1Download from Server 2Download from Server 3

For Minecraft 1.7.10

Download from Server 1Download from Server 2

For Minecraft 1.8.0

Download from Server 1Download from Server 2

For Minecraft 1.8.9

Download from Server 1Download from Server 2

Author: DrZhark