I'd say splitscreen COULD work right now. There is one massive problem, though: controls... you need 6 for moving and 10 for weapon changing, and usually at least 3 are pressed at once (and it may be even 4!). Basically, you would have to have 2 keyboards avaible. Also, one player would just sit near right spawner, second one near left ones... right now the game is balanced for just one player, but technically it is possible to make a good coop map.
TTFTCUTS: Limited time during the boss fight was meant to make camping a little bit harder. I know how to fix it, simply, second boss will arrive no matter if the first one is already spawned or not

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