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Nice. Try making projectiles bounce off of walls with rebound, if you don't like that just have the harder version be a new game plus (Last portal starts you over?). You can have text displays on the ui show health. Just have global variable or player health variable and have it display status every tick. You need a text thingy whatever it's called, and put it on the screen on ui layer where you want it seen. Now you can add level, score, bad guys, or whatever else.