Wish I could scroll left and right with the arrow keys, and way faster than panning with the mouse. Really frustrating when fighting the boss. Also, being able to lock the mouse to the game window (so it doesn't leave the border, click elsewhere on the browser, start scrolling and panning as I try to slash, etc).
Collision checking is a little weird; sometimes I swear I miss the jump, then end up on top, other times I don't think I get hit and am dead.
I second everyone else's vote that "higher jumps make late game tricky" is stupid and we should be allowed to not jump as high as possible every time. It shouldn't be easier to complete the game at level 1 than level 11.
@Sindarin8 You need to get him to miss the ball in order to score points, not just keep it out of your own side. Hit it with the side of your paddle rather than the middle to get it to bounce at weird angles, and use your weapon to cause them to reflect midway through the field, causing him to miss more often.
Pro tip for the hard badge: Don't ever take a boost. Don't use your natural ones, don't try to hit the flying ones. Just steer well, and learn to love "brakes".
To vastly improve your bouncing accuracy, don't think of it as a mirror but just another cannon that you load and instantly fire when you get hit in the shield. Put your cursor on the front of the tank you want to hit, and it dies. Just make sure you're still catching the shot.
About the golden surprise badge: You need to actually find the wizard in the wild (I saw him in area 21, maybe he appears in other places) then defeat him for you to win and complete the game. Finding the robot isn't enough alone.