Did not notice this thread was created until now, right.
The first level looks a bit simplistic and could've been better. I found a few breaks which can be fixed with a few tweaks. At 1:17, I don't think the key is needed to enter the door... Before shattering all the turn blocks, you can hurt yourself at the exact time you get to the last block.
And after pressing the P-switch found at 2:16, you can use Yoshi to regenerate it by licking it at the same time it's pressed. Thus, no need to use him afterwards, because you can keep the P-switch and use it to jump to the gap above upon entering the pipe. Kudos to the mole part, it was neato.
The second level doesn't have much going on. You focus on just Yoshies, which makes the level look repetitive (not to mention the glitches used have been overused to death already...). You can also enter on doors that are one-tile wide with Yoshi. I suggest you think of an use for enemies that work well underwater, such as Urchins, Rip Van Fishes, and so on.
By the way, the name "MMD3" has no accurate representation to this hack at all, or it'd have more "do or die" puzzles and be even more difficult and glitch-abusing than the first two installments to the point it'd become almost pit (and no way I'd make it either...). I find "Mario's Unexpected Catastrophe" more fitting. I wish you the best of luck with this hack!
Eh, to be honest, this looks like "see what other hacks have done. use their ideas. don't mind if they aren't connected to each other at all. done.". The gimmick is never consistent: it keeps to change and change. The FLUDD idea was good, but you didn't really use it much and just changed the gimmick. Again. This may be just me; but I think the gimmick should be consistent. If not, the gimmicks at least should have a connection.
Also, using the same colors for the background and foreground isn't the best idea.
Cut down on the waiting, dude. First you have to wait for the tide to rise at the beginning, then later you have to wait for the Porcu-puffer to take you to the door, and possibly more I can't recall. Your levels could definitely use a lot more action.
This level felt more toward the "very easy side", honestly. The FLUDD gimmick, while it's a nice addition, could use more action than what was provided. The dolphin section, for instance, can be done without it, because as the dolphin jumps, you can jump (normal, spinjump, whatever) to maintain the tide due to it having vertical scroll enabled and that's about the whole room. Try playing with tides and even the aforementioned custom sprite (you could hop until the counter decreases to one and there's barely any water around).
That water glitch room could have more fishes or something to increase the difficulty even more. There are many possibilities with the fact that you're not underwater while the sprites act like they are. It's just a personal opinion, you don't need to feel unmotivated by what I and others have said.
I think so far these levels have been too rushed and too easy. So I'm starting fresh. I only get the weekends to use my computer now that I'm back home and break ends in two days. So expect less action on this. I will still be working on the kaizo collab however, and I'll put most of my energy into that.