Like Kumasylum in Tera.

Players control Monsters and fight other players. No Grand Company restrictions and you get to have chests that drop in them like dungeons as well as tokens and unique gear to them.

You can have many different types of these dungeons and since they are balanced around a party like normal PvE you can do it with a normal group, players just play the monsters!

This means the game would be a lot more fun and balanced.

Maze Race
Imagine a game where 8 players challenge 64 (Monster) players in a large maze. Monsters have to find players and squish them, players as they go deeper in the dungeon get chests and its like a gauntlet.

Cat and Mouse.
Imagine a game where 64 players challenge 8 "Giants" and the Giants are players who go around killing and crushing people. Players must band together of course the Giants have to separate because if they are standing next to each other players can scatter around and complete objectives.