One of the first things you see in 1-1 is a simple tree, you mightn't think much of it, yet it has been known for a while that it's collision can be a little buggy.

I had used version 1.0.3 for this IL but it seems to work in other patches as well.

To perform this skip, you might need to run the start of 1-1 at about 200FPS as it doesn't work at 60FPS, and I haven't tested anything in between. It'll also be good to get a feel for the tree, walk around it, walk into it, jump into it, etc.

I first line myself up 1 block to the right of the tree and walk forward. As I near the tree I take a medium fast turn as to preserve momentum, and hug up against the tree. While rounding it, I'll line myself up with the far back left corner and continue forward. Pressing "Space" to jump is not needed, due to the collision of the ground and tree, you'll be launched up into the air at an unfortunately variable speed, all while hoping to land on the roof in front of you.

With this in mind and time to grind, this is useful for all 3 categories of 1-1.

Note: This can be improved, at the start, you can walk straight ahead and take a sharp left as you hit the tree, with luck on your side, you'll get the height you need.