Volfy

Hold Space and steer off the edge to draw a line through open ground; reach an edge again and the side without the boss is yours. The edge is safe, the line is not. Ten rounds, each with its own boss and its own hidden picture; grey boxes hold gifts, a red one a cannon that can shoot the boss down, and a timer runs while you dither. One player or two taking turns, and a top five kept in your browser.