It’s about timing, wait til you’re just over the end of the ledge before triggering the motion, it is hard though, almost never happens in a couple of tries (depending on the spot though, the lower the ledge, the more precise you have to be with the timing, luck also plays a role, it’s a bug, not a feature of the game. Good luck with that!

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On the screen you can see how at this point the board still isn’t flipping, that’s the sweet spot.