The Royal Bumble.
Have GMs/Devs create an item with knockback possibly with unlimited charges.
Have it take place in a square arena, if players are knocked out of arena they are eliminated (Players can police this and GMs can DT people knocked out). Also could take place on a Kelethin platform, people who are knocked off are truly eliminated.
Two players start in the 'ring' and then another person is added every 30/45/60seconds.
Order of players that start in the 'ring' and enter the 'ring' afterwards is decided by lottery or /rolling before hand.
Bonus points: Have 30 people sign up before hand and send you their intro music.
Have a countdown for each player to enter the ring. Play their intro music as they run to the ring. Kelethin ramps would make a nice runway for players to make their intro. Although might be hard to find a good Kelethin platform for bums to fight on and people to spectate.