The game has 5 levels/stages.
For some reason, the game text and menus are stated as "undefined".
Start screen top selection --> Game instructions
Start screen bottom selection --> Start game
Instructions: Use the mouse to move Robot Boy, click to attack, and spacebar to fly off the ground and dodge enemy attacks.
Destroyed enemies drop green balls (points) and batteries.
Collect batteries to fill the meter on the left, powering up Robot Boy and allowing him to shoot lasers and later homing rockets.
You have 3 lives for each stage, watch the health bar on the right; although it will slowly regenerate, depleting it completely will cost you 1 life.
