You probably figured this out from watching the runs if you're planning to run this, but there are two skips: goat skip in Locusts, and mask skip at the end of the run.

Goat skip just skips luring the praying mantis to the goat, because his eyes give clues that you don't need. You just drag the fireflies to the correct positions, which aren't too hard to find, and dig in the right spot.

Mask skip skips most of the ending sequence where you go through the island and put the masks on everyone. If you spam the back button after you get the cube, you can get back up the well to the altar area, which is supposed to be impossible. It's not even very hard to pull off, although if you go back one too many times you'll have to lose time putting the deer mask on Nicholas. Note that you still need to collect the masks to open the door in the cave.

Also note that 100% does NOT use either of these. If you do goat skip, you can't get the eighth symbol. And as far as I can tell (as the only one who's tried), mask skip doesn't work if you get the owl mask first. If you can get it to work, I'd be very happy to be proven wrong.