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.
Installation:
- Just download the .zip file and put it into the /.minecraf/mods/ folder
Changelogs:
v2.3.0
- Updated beta version for Minecraft 1.6.2
For 1.6.2
http://www.dl2.9minecraft.net/index.php?act=dl&id=1376952502
http://www.dl3.9minecraft.net/index.php?act=dl&id=1376928048
For 1.5.2
http://www.dl.9minecraft.net/index.php?act=dl&id=1368599912
http://www.dl4.9minecraft.net/index.php?act=dl&id=1368574741
For 1.5.1
http://www.dl2.9minecraft.net/index.php?act=dl&id=1365675384
For 1.4.7/1.4.6
For 1.4.5
Credits: DrZhark
Source: Custom Mob Spawner Mod for Minecraft 1.6.2/1.5.2/1.4.7