I saw this event in another server.
A sudden message pops up saying 'Monsters have invaded prontera city[or any map]'
Lot of custom mobs gets spawned there.
We gotta find 3 custom mini bosses and kill them,which drops 5 event coins[or coupons]
When you kill the 3rd mini boss,another message pops up saying a major MVP has been spawned.The mobs keep on spawning till you find and kill the major MVP boss.
If we kill the mvp, it drops 15 event coins [or coupons].Name of the player who got mvp while killing the major boss will be broadcasted like "xxxx has saved the city from invasion".
To spice up the event a custom equip can be dropped or a custom mvp card with good attributes.This will motivate players to participate in the event.
Forsaken ro had mobs spawning on halloween/xmas,but it just drops candies/goodies that gives some temporary buffs and it didnt have custom mini bosses/mvp.But this event is more than that.
If this event is hosted i believe lot of players would encourage it.