I have been thinking that maybe on Minecraft, that there should be a texture pack for madness. Make the sun red, and give the landscape a reddish tint, and make the moon all cracked up or almost faded out and dark, and the zombies given a madness makeover, the skeletons almost decaying, and the creepers... madcreepers.
Also, if you have experience with texture packs, wait untill around 1.8 to work on these ideas.
Nomaron
There practically already is one. Plus I'm making my own texture pack :3
What about pigs and cows and shit.
FallowerOfHank
As fo the pigs, we could do an easter egg and try to put the hot dog vendor in... Chickens... IDK. Cows? Ummm, IDK. Skeletons: Give a mad feel. Zombies? Obvious. The rest is up to you guys!