For whatever reason I can't seem to figure out how to get the super jump on Mountaintop Retreat to go high enough to get the skip and clear the level. I've looked at a couple of videos that get the jump and it's hard to tell what I'm doing differently. My guess is maybe my initial jump into the super jump isn't high enough?

Here's a clip of me falling short on the jump:

You can see in deathpony run at the start instead of jumping on the top after getting the super jump he goes back down a level and jumps on ramp up- . Have fun!

The method you are attempting is pretty difficult. In your clip, you seem to hit the top edge of the platform, which usually doesn't give the right height or direction. You instead want to slide straight up the side of the platform.

Additional tips: make sure you jump + SJ + blast in that order and in very quick succession. You want to maximize your vertical speed (1) for max height, (2) so your horizontal speed doesn't cause you to bonk and fall backwards when you instead want to slide.