The Blokkit Mod adds in pet blocks that level up and evolve!
In this 1.6.4 Blokkit Mod Showcase:
This Minecraft Mod adds pet blocks into Minecraft that will follow you around and fight with you. One of the cool features of this mod is the ability to level up your pet and it will get stronger. Once it reaches level 5 you can give it a golden apple and it will evolve and grow bigger and stronger.
Get your Minecraft Mod here: