We all know the skip on level 6, where you jump across the death plane to the finish, it's easy. But is this viable on any other level? (without the levels where the death plane is above ground, like level 29).

The only level I know that this might work on is level 27. But doing even a single jump on the death plane is hard and jumping a second time I haven't even done.

it used to be viable for level 10 (it still is for sr4 classic) and sage found a different version of the level 27 skip with it, but i don't think its useful anywhere else

Level 10 is still doable with a speed coil. You can jump on the death plane once, as long as it is grass and not the other plane, and though it is hard soon you can be consistant

you can jump on the death plane near the end once on 10/11 but it's not viable for any skips that we know of and i doubt it could be due to how linear those levels are in peach desert dimension you can't jump on the death plane in most levels, even if you can it's not that consistent most of the time so i doubt we'll find anything new for a while unless there's a major update or change