I also got stock on the A+B Part. I did think it was cool that the platform stays in the same place after you die. It is an interesting way to add complexity to the puzzles.
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That's because that's just the tutorial area and it's supposed to teach you how to play, so you don't actually die, you just get teleported back to try again. I'm going to have to put up some visual guide up to show people how to do that last part, but you are supposed to quickly tap A and B, or Space and L at the same time while moving right. If you don't tap fast enough the platform will move out of the way and you will fall.