if you're in need of some original ideas i listed some i initially wanted to try myself.
Boxing events: 1v1 tournament mode, ubers: you can only use punching based moves (sky uppercut, thunderpunch etc.)
Rock paper scissor tournaments: self explanatory. Not the most entertaining kind of event, but they're pretty quick. Ok, it's a pretty bad concept, but i'd personally give it a try..
Beauty contests: you're gonna need at least 2 impartial judges to help you
Regular tournaments are a safe card since pretty much everyone who's into events likes them.
As long as your events are reasonably short and fun people should come.
No need to say the reward plays a big part too; i'd personally try to keep the time/reward balance as close as possible to that of our official events (or even higher if you feel generous).