April 1

Switch off RPG for the day, and see how people get on with the new monsters?

Find one skin, like a white fluffy rabbit, and set everyone's skin to be that one. Players and Monsters.

Mix the teams up, so some players join on the monster's side, and some monsters join on the defending side.

Extend the monster master class so it can spawn vampire gnats/ lava skaarj/titans/ghost skaarj etc as pets.

Give everyone, including monsters, slowfoot -10, and make all weapons force -5, including the trans.

Enable some of the built in mods, like bighead, low gravity etc.

Modify wave 16 to be against a really big boss monster.

Create an interaction that randomly draws other stuff on it. Like a snow shower, flowers growing, butterflies, white rabbits. Sometimes switches the lights out for a few seconds. Sometimes goes foggy.
Just to make it difficult to see what's happening and distract the player.

Start each map at a random wave, rather than wave 1.

How about getting the AI to drive the humans, and have players controlling the monsters? So you spawn as a skaarj or nali or warlord.

How about changing all the monsters to turtles, and give us hammers for weapons?

How about a mod where when anyone scores a kill, they get frozen for 2 seconds?

How about changing the InvasionSpree to give all sorts of extra "bonuses"?

Have a "key scrambler", so that when you get hit, for the next second you are dizzy, and your movement keys do random things.

How about playing different games for the day. Jailbreak, Mutant, CTF etc.?

How about each time someone connects give them a random set of stats, similar to the way a bot gets their stats. So this time you could be playing a LW level 130, next a Medic level 10, then ....

Or just start everyone off with no stats, set the levelling requirement to say 50+10 points per level (so level 1 to 2 would be 50 points, 2 to 3 would be 60, 3 to 4 70,...,30 to 31 would be 340 points, ... 80 to 81 would be 840 points etc) and see who can get to the highest level in one day? Reset at end of day.