Anything with the Munchkin line will have the same backing. Munchkin, Munchkin 2, Munchkin 3, etc. Each of those will have a subtitles such as Munchkin 2: Unnatural Axe. If it has any other word in the title other than a subtitle such as Cthulhu Munchkin, Space Munchkin, Munchkin Zombies, etc those will have different backings and variant rules. Either way they are mostly the same game, I have been playing Munchkin since it came out. Its a great game but eventually gets old, the best variant is the theme that appeals to you since the games are largely the same, for me thats Cthulhu Munchkin as I am a big Lovecraft fan.