Arrows keys. I have made a sequel to this game that has more levels and mechanics, so if you get bored of this one, go check it out at: https://scratch.mit.edu/projects/124304799/
Okay, I know a lot of people have said in the comments section that this is too short, and I agree with you. I made a sequel with more levels, but this one keeps gaining popularity so I'm making a large update that will include a lot more content being added to this game, so I hope that this will make it more deserving of all the attention it's got. Thanks for all the support, it really means a lot to me! :)
