I think the best I can recall is where two teams are picked - the DM has a list of bosses that are spawned one after another (once killed) for each team, first team to kill all the bosses wins. Or capture the flag worked quite well, if the teams were nice and even.
I remember this one. I had a prize to the team who 1st beat A or WK. The only issue was that one of the sides had more powerful bosses than the other so I had allowed each side to pick 5 and I choose 3 or something like that to balance boss selection. The other issue was that you really needed a minimum of 5 ppl on each side to make it go quickly.
If I have time after I get all my RL stuff cleared during the day I might run another similar event ... this would mostly be after 9:30-10 pm NY time.