Just throwing some ideas around. My new idea for an event combines ideas from time attack, hordes and Occult.
Rewards: Reaching certain Milestones as well as ranking rewards to compare with other players
- Unlimited enemies 10:00 minute timer.
- Unlimited enemies no timer (Death sentence and sleep are banned)
- Hellmode: unlimited enemies but purely revenge monsters. (Payback Killer banned)
I think this would be fun because it would encourage players to get really creative. Devs can buff mons as they see fit. (Maybe monsters progressively get buffed).
Also if it needs to be padded out a bit you could make the first option specific to element types. But it would be a nice - non grind event as it is.
Not sure about the name? Mega Challenge Battle