Go to the spawn of level 3 then teleport to level 1. If you get luck and spawn in one of the 3 middle pads you'll start with a good amount of speed. Can we use this in a skipless run because there are no skips in it?
When you jump on a booster and hold down w once you land you gain speed that can save you about 3 sec. It's really fast so you need to be prepared(You can fall off easily).
Just some fun ideas for challenges
Any% No Blue Shells - All power-ups except blue shell
No Backwards - No running backwards(does not apply to down to up levels and scroll levels)
All Bosses - Can use shortcuts but once you defeat the 9th boss(doesn't need to be in order) you won(World1, World2, World3, World4, World5, World6, World7, World8, Bowser's Castle)
I'll add more ideas later. I don't expect them to become categories but they could be some fun challenges.
On w2-3 they're is a maze of the moving wall things(idk what they're called) that has a piranha plant in the middle. Every 4 times the plant bites it stops for about a second. if you're on the left side of it when it stops biting you can run and fall beside it without dieing and keep going. If someone timed it perfectly in a run they could maybe save about 2 or 3 seconds at most. It probably wont help i just thought it was interesting.