April 1

How about having games of team deathmatch, and make each player at the start level 50 or 100 or something, so they can choose what class and skills they are? And increase the monsters available to be summoned to include gnats, titans, lava skaarj and poison queens.

At one point I remember seeing a team invasion mod, where you had two teams of players against the monsters. Either the monsters won, or the highest player team. edit: here

Perhaps add battle bikes etc, as listed here

Add Vortex's weapons?

Set the InvasionAutoAdjustFactor to 0.5, up the monster skill by 1, and the ExpForWin to 1000.
Oh, and set bIronManMode to True.

Quick and dirty. I'll leave comments mum so the non-coders won't get it right away