I have decided to try to tackle all challenges. Mixing 2d and 3d with a single asset pack is not the most difficult combo, as you can grab a 2d asset pack containing a tileset, and use the tiles as textures for your 3d world, while using the objects as 2d sprites like in the old boomer shooters.
However, making a coop game that can be controlled with a single mouse is kinda impossible for me. Local coop could only work if one player uses the left button, and the other the right, which is ridiculous. A multiplayer coop is a bit hard to pull off in 48 hours, especially since I never made one. :D And the no text would make it even harder to allow players to join the same session. :D