Some things I was thinking that could be added is an upgrade for the bow. Have the ability to shoot an arrow which explodes into shrapnel kind of like a spidertron grenade. This would actually make bow builds viable later against Mark 3 robots. A drawback for balance could be it uses a lot of your energy. Another thing I thought of was you could dual wield swords which would have 2 benefits, You could jetpack and be able to slice robots from 2 sides, and you would be able to block arrows with one and swing with another if you chose. The very last feature isn't an upgrade but how about in Endless you get the bow to start of with? Thanks for reading!