This came at me out of the blue this morning while thinking about the gauntlet-style gameplay of things like L4D2 finales: would it be possible to create a sort of reverse-MVM type map where instead of sitting somewhere and killing the robots coming towards you, you have to progress through the map with robots coming forward against you? Anyone who's played the custom L4D2 campaign Carried Off should know what I mean - the finale involves fighting all the way up an office building against an almost constant flow of zombies, which makes it great fun for teamwork, ammo management, route planning, etc. I'm not too familiar with what's possible and what's not within an MvM map since I've never made one myself, but I was thinking one of the players on the team should take the intel to certain checkpoints to unlock them, and each checkpoint represents a new "ready-up" period where you can cool off and buy upgrades etc, and after each checkpoints the robot waves get harder. If you get the intel all the way through the map then you win, but if you run out of time getting it to the next checkpoint then you lose. I guess this would involve making each wave last the total amount of time on the round timer for each round, and if the intel was delivered early the wave would be terminated. If the intel's dropped, it has three seconds before it's reset to the last checkpoint. The hardest thing I think would be to ensure that the players spawned in the correct checkpoint room for each stage.