In Runescape, there was a minigame like that called "bounty hunter", and adaptations of it have been put into wow servers. It also is a staple of the Assassin's creed series: Hunt faster than you're hunted.
(non pvp realms) - Ganking Contest (track killing blows of raid via script, and force them all to stay in a dud queue to prevent bgs). Give them 20 minutes starting from their home city to find and gank as many people as possible.
Rifle War - Low (or high) levels (perma-silenced) enter a battle where they can only use the pee-shooting rifles. From there, it's just last man standing. unlimited ammo.
Evolved - Essentially like the game. One player in the raid gets a Massive Health and damage bonus, and is turned into an enemy (preferabbly forced to take the form of a famous wow character of that class), and the killing blow gets a point, as well as the new "evolved" status. after a certain amount of time, the game is called, and the person with the most kills wins.
I had another idea....
Spoiler:Show