Kind of similar to Fluffring or the Halloween Event Boss, it'd be cool if we introduced World Bosses to the server.
World Bosses would be difficult mvp type monsters that spawn at random times on random maps and provide good loot or costumes to whoever was actively involved to kill it. The idea is that this would be something that whenever it spawns the people on the server can come together to try and kill it. Like other implementations of world bosses i've seen on other games, the world boss should be incredibly difficult (even causing a lot of failures) and fun requiring some level of group effort (ressing, buffing, warp portaling, land protectoring, etc. etc.).
I believe there's already some mechanics that exist that check for afkers in some of the events, so that can be used here too.
But yeah at the heart of it, I think world bosses would be an exciting little event that will let the server come together to fight the boss to get some cool rewards.