Have you ever wanted to hatch mutant creepers that can become your minions to aid in your attacks? This is a very neat mod that adds a whole new dynamic to mobs in Minecraft. It allows for rare but random spawns of mutated mobs. To spawn one manually this mod also adds a new potion, Chemical X, which when thrown at a mob will either mutate or kill it.
*** Not affiliated with MineCraft or Mojang. ***