I know what to do know. Find the mural and the switches before the part you get the bomb bag. Switch them in the order on the mural and use the expandable rod to get to the button, press the button and a ladder will appear. Do a challenge and you'll get the Angel Boots, they allow you to double jump.
And even *I* was stuck when I was translating it. I resisted the urge to ask Push (the creator) and figured it out all by myself. It seems he's most proud of this trick, second being the fleeing expandable rod
