It occurred to me that the Fluxx and Munchkin are quite similar games in that they are casual games that derive their fun from their theming.
Is it possible to combine the games?
As much as I love Munchkin and Fluxx, the game mechanics are so different that combining them would just cause a headache. How would keepers interact with Kicking down the door? Do goals change the requirement to reach level 10? It would be so confusing and weird to play that I would suggest staying away from combining these card games. However, there were expansions for both games if you want to freshen up gameplay.