Royal Rumble: 5 Players - free for all -
Hardcore: No armor, weapons, cores, boosters, just skill.
3v3:... 3 players vs. 3 players
Double NPC: Two NPC's against what # of players, preferable 2-3, at most 4.
Testing: Players are selected to help with testing, player is put up against a mod, or person of that sort; only available for certain updates and events.
Hulk Smash(idk what else to name it): TWO juggers, and five 'newbs'.
Class Clash Certain, and/or same classes against one another in 1V1 and 2V2, or even Jugger.
Disable Random Random things are disabled, boosters, cores, certain skills, etc
Mix & match
Hardcore mixed with Hulk Smash? Juggers without anything but skills, but 'newbs' have disabled boosters.
Royal Rumble & Hardcore
Hardcore + anything pretty much, lol.
Well that's all I could think of in 3 minutes, replay for any of your ideas also! (: