I loved this! I enjoyed the ??? and the double jump, and also managed to accidentally beat the game without either. I also enjoyed the fact that each power-up is in an area where you need to use them afterwards to clue the player in on what they can do now. Though, I have no idea what the green coin did. Two suggestions: Each power-up could look unique in some way, maybe a different color on each coin? Also, telling the player what they unlocked in some way (maybe a pop up menu? maybe just some text on the bottom that fades away?) could help, as I was confused as to what I got for collecting the double jump coin.