Here's a link to a very fun mutator that was made for 2K4. It's called GunGame, and it's been popular in games like Counterstrike for years. Basically everyone starts out with an assault rifle, and with each kill they get a new weapon. So after you kill someone with the assault rifle, you get two assault rifles. After you kill someone with those, you get a bio rifle, and so on and so forth. The player who cycles through all the weapons is the one who wins. Players also have a shield gun as well, and when you shield gun someone they fall back two levels (e.g., going from bio back to assault) There's even a team mode in this as well, where a team wins by having one of its players first cycling through all the weapons. Think of the teamplay options such as protecting your highest level player from being shield gun killed, or going after the highest level player on the other team with the shield gun.
I tried it in instant action and it's very fun.
