There's a bit of a glitch in Water Santuary. At the area just after the Torpedo Ted launcher, there's a mushroom block under some invisible blocks (presumably to prevent cheesing of the level.) However, there's a 1-block space beneath the invisible block that's farthest right that a player can squeeze into by crouching and jumping.
If the player looks to the left and stands up, they'll slide through the wall until the next space where they could stand up, like so:
The easiest fix is just to put an invisible block in the one-block space.
All in all, this was a fun level to play. I can't for the life of me remember how to do a formal review, although I might look into it and come back later with one