Would it still be valid if I used only the mouses movement but no other button or keys for input?

Well, it's obviously not a 1-button game =) and not really in the spirit of the jam (mouse mouvement is roughly the equivalent of 4 directional buttons), but that could still be a interesting constraint. If you have a good idea with this gameplay, go for it, a game is still better than no game!

Thanks good to know