Use arrow keys or wasd to move, use the 1 and 2 buttons to switch guns, and p to open the shop. Shoot the zombies to earn money. If you survive long enough, you will get 1-Ups. It will get progressively harder as you go. WARNING: I just love to make my remixes a lot harder than the original, so yeah.
Music from exit path, exit path 2, and collosatron. Don't mind the random intro :)