So far, there are 8 bosses to fight in the game: Remy, Linnea, Mushna, Dorlly, Wuelie, Long Leg Sprinting Trumpet Mushroom, Momo, Cynthia. There are a bunch of side quest but most of them are incomplete at this stage. You also cannot enter the Mushroom Village yet but will be able to in a future update, once you fight and defeat the blue mushroom girl. If you've defeated all the bosses so far, that should be all there is to do in the game at this point.