Hey, could someone give me a hint as to where the blue key is in this one? I feel like I've run through the entire world a number of times with all my abilities, but still can't find a clue to that one. Thanks!
Spoiler: (click to show/hide) After pressing the button and changing the world. Head to the far right and jump to the right from the pillar of semi-invisible blocks. There is the void screen.