I like the idea as well, same issue with the controls being too complex doing 3 different types of control on limited time constraint right off the bet, if you are keeping the fire/lava idea, best simplify the controls to just arrow key and space bar, or just WASD/arrow for directions with mouse (right click for jump and left click for punch might be doable) ; if the beginning there is no fire coming, allowing the players to get used to the control and present a more gradual difficulty curve,  the idea might work for a much slower pacing game.