This level was tough! The gimmick was executed greatly, but there were some things on the level that bothered me.
1. Coin inconsistency
At the beginning, there were some
SMB3 coins as a reward for an optional challenge.

But, right after that, there were
SMW coins!

And, a little bit later,
SMB3 coins again, whose setup doesn't quite follow the player's path and could be easily repositioned.

And then no coins for the rest of the level, which also bothers me a bit.
The thing is, I'd recommend using only one style of coin per level to keep it cohesive and coherent.
2. Lack of power-ups
This level was hard to get through! You should've put some power-ups to help the player along the way and adapt some setups to big player size. The lack of power-ups made the level frustrating so it had to be completed with perfection. Levels with a fair difficulty increase the player's engagement and enjoyment.
I'm guessing you wanted the player to be small, though, because of the setup just after the checkpoint which would supposedly force a big player to take a hit (but can be easily cheesed with a crouch clip)
3. Lack of variety!
This level, although it's hard and exciting to get through some parts, it's boooring! You have to do the same things over and over and over and over and over, with just some minor changes! Why don't you try placing some coin-collecting or easier segments between the hellish platforming sections to work as breathing room? That way, the level would be more varied, and it could flow better. You could also try adding some changes to the gimmick, say, why don't you have
flying enemies instead of platforms for a few setups? They're also one-try, but you can't stand on them! Brainstorming a bit about the way your gimmicks work is a way to revamp them.
4. The Ending.
Even though it was fun seeing the dry bones falling into lava after the infernal dungeon I just went through, there was the troll.
just
w h y
If someone ever fell to that troll (I thankfully didn't), they'd have to restart from the checkpoint! That is
EVIL! Especially in a level like this!