Mutant Creature Mod to create Chemical X

[Katkasper]

I am very new to this whole world. Trying to get the Mutant Creature Mod for my son so Chemical X will work. New at this, I was told the Forge version and the mod needs to be the same so they are both 1.6.4, I did as instructed and placed the .zip in the mod folder Forge is on the game when I open it, hit play and get an "Error Game Crashed - The game crashed whilst there was a severe problem during mod loading that has caused the game to fail
Error: cpw.mods.fml.common.LoaderException: java.lang.NoClassDefFoundError: thehippomaster/MutantCreatures/MutantSkeleton"

[Yunus1903]

1.6.4 is no longer supported on this forum.
Please update to a more modern version of Minecraft (1.14+) to receive support.