I remember playing Maplestory back in the day during a Christmas event admins summoned these large stocking bosses that dropped alot of stuff, they didn't deal a lot of damage and everyone could deal damage to them, they had loads of hp that took collaboration and time from everyone to take down. I would like to see something like this in a summoning sack. Something with high hp, that everyone can hit that once defeated drops random loot maybe even have a small chance of an epic drop. The brand new monster galore is the same old thing and doesn't bring out the same level of fun event feel that this sort of boss does, noobs cant fight strong bosses but this they could and come out with some decent loot.
The issue is the server can't handle the amount of ppl in 1 map, that's why in events they limit the number of ppl per room (well partially for event boss not to die too quickly too) The last time they summoned something like pink bean in lith harbor that I joined, you'd be dcing more than dying, both which are quite frequent.