What RPG would you use to run Adventure Time?

[imurphy943]

Adventure Time is a cartoon created by Pendleton Ward and produced by Frederator. The show is set on Earth "after the bombs have fallen and magic has come back into the world". It features really weird monsters and weirder people, several mutants, some magicians, dungeons, D&D references, ancient and recent technology, usually infused with impossibility, and one 'Conan the Barbarian' reference.

My question to you is:
What RPG system would you use to emulate Adventure Time, and how would you alter the rules to make it more true to the source material?

Please name your system, describe it in a sentence or two, and give the house rules you would add.

 

[the Jester]

Gamma World, no changes necessary.

Bam.

 

[Whizbang Dustyboots]

Labyrinth Lord/Mutant Future -- it's old school D&D with Gamma World rules added, which is pretty explicitly what Adventure Time is supposed to be, and appropriately breezy and rules-light.

 

[Yora]

Risus?
Making up as you go.