In my Aprils fools 14w13d snapshot reveiw I used a texture pack that turned

Zombies = Aliens
Gold = Amethyst
Diamonds to Emeralds
Rotten Flesh = Alien Slime
Diamond tools and armor = Emerald tools and armor

Video: https://www.youtube.com/watch?v=y8gHUmfeKyA

for mars I put a comand block with this in it /tp @p[x=x,y=y,z=z,r=10] x y z
which teleported me to an area in the world that looked like mars :P

Channel: www.youtube.com/user/devinator19