Gunpowder... Spice... And everything nice. These were the ingredients chosen to create the perfect creeper minion. But Professor HippoMaster accidentally added an extra ingredient to the concoction... Chemical X! Thus the Mutant Creatures were born
Screenshots:
Mutant Zombie



Mutant Creeper






Changelogs:
v1.1.0:

  • Increased mutant creeper health to 60 hearts
  • Made mutant creeper explosions do more damage
  • Made mutant creeper's melee do more damage
  • Increased the chance of mutant creeper using lightning instead of healing when doing charge attack to 1/8A
  • Added mutant zombie
  • Added zombie minion
  • Added hulk hammer
  • Fixed heart particles not spawning
  • Verified SMP compatibility
  • Re-added config file

Installation:

  • Extract the mod zip
  • Locate .minecraft
    • Click Start and type %appdata% into the Search area
    • Click the folder that is called Roaming
    • There should be a folder inside called .minecraft

  • Move the mod zip file to .minecraft/mods
  • Play!

Requires Minecraft Forge

Source: Mutant Creatures Mod for Minecraft 1.4.4