The 2nd shortcut in Moon Grotto saves 1:00 to 1:20 depending on how efficient you are at getting the jumps. I did 5 comparisons and the most time i saved was 1:18 and at worst i lost 6 minutes... dont ask.
The iceless jump MilsTailsPrower showed off is pretty challenging. The first jump to reach the wall is probably pixel-perfect and requires very precise turn timing in midair. Jumping off the wall when you hit it is probably not frame perfect, but it's damn near. Jumping across to the next platform is deceptively precise, and you can easily miss it. You need at least four health to damage boost through the spikes, so you'd better not take any damage from the slime. All in all, I have to commend you for even finding this in the first place, let alone being able to do it at all consistently.