For the double reverse warlock punch, remember that you need to reverse it twice.
You need to realize the difference between a reverse B and a B reversal:
- A reverse B is flicking the control stick in the opposite direction, and then pressing B. This makes the B move come out in the direction you flicked, but doesn't change your trajectory.
- B-reversal is when you perform the B move, and THEN immediately tilt the control stick in the opposite direction. This also makes the move come out in the opposite direction, but it also usually completely stops your trajectory and makes your character move in the opposite direction. In warlock punch's case, there is a "turning around" animation when Ganon B-reversals the punch.
To recover with warlock punch, you need to do both a reverse B AND a B-reversal. So once you get launched offstage, you need to flick the control stick away from the stage, press B, and then immediately tilt the control stick back towards the stage. This way, Ganon starts his warlock punch in the opposite direction, and then reverses it again with B-reversal to gain momentum.
To be honest this really isn't that useful... you should get edgeguarded every time you try to do this. But sometimes it's the only way you can recover, like if you don't have a double jump left. Also, I'm pretty sure the momentum canceling makes you survive a few %'s higher than momentum canceling the regular way... though I haven't tested this.