Here's what I can think of:
Super Mario Flash 2
Something to this effect is SMBX which was thankfully shown to me by Ducky Duck er yeah's topic
It has 2 player co-op along with a battle mode in which you kill eachother, AND you can do things to people while they're playing, if you were to do so on the level editor. You'd have to keep a score yourself though, on what I'm not sure, perhaps kills.
Also iunno, Trials (any of them I think, perhaps fusion kicks your licks) has a fantastic level editor, if I can recall someone even toyed around with evolution and made like a gun game thing.