Lots of things you can add here, first you can add a Pause Menu, where upgrades are, to sum that add Level Up! above the spaceship when you level, try putting in a World Map, where you choose where you want to go, and of course you can add much MUCH more upgrades, like a bullet scatter (fires 3 bullets instead of one) later it fires more bullets, a Power upgrade which makes your bullets a different colour and it inflicts more damage, say like level 2 is yellow, level 3 is orange, level 4 is red, and MAX is black, you can just swim in all the Updates
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