Arrow keys. Get to the end (Green flag). Press C to open the customization. V to open the achievement menu. Avoid looking in the code because there are secrets that will be spoiled if you do.
This game is quite a bit more difficult than the first game. Like I said in the first game, "It is possible. It is, however, a rage game. Do not shout at me, for you have been warned." Game 1 here: https://scratch.mit.edu/projects/853188882