the oddball you mentioned on that level is actually on every level in a deffernt place, and each one has a different effect.

For example:
on delta halo, the one there (don't remember how I got it) lets you turn invisible as the masterchief (like the arbiter does) called envy

On one of the arbiter levels (the one where you start off fighting lotsa sentinals) go backwards at the start and it will screw up explosion physics so everything flies 5x higher when it explodes (good with grunt birthday party) called sputnick
on metropolis, if you jump on the roof, you find thid one that makes you fight a lot of black elites-not sure what happens after that because I die everytime, but w/e

these are the ones I've found-keep looking fo the others