May as well post a couple of my level codes here, I'll snoop around and have a look at some of yours later, too.

I've made something like 12, but these are probably my best ones.

Great Rails of Fire
539E-0000-0034-FC3B
I made this one a while back - it's got an interesting mechanic involving synchronised firebars.

Towering Inferno
CFF8-0000-002D-5E18
This one also uses firebars, but as part of a much larger framework.

Koopancakes
7553-0000-003D-B05E
A puzzle level. Can you figure out how to escape?

Ice Climber
37CA-0000-005F-FF6D
A SMB3 ice level. It took quite a while to disguise the fact that it's set in the plains area.

Job Security
6EDF-0000-0075-C13E
A journey inside the mind of a 30-year-strong genocidal mercenary.

Yeah, the 3 koopa part has many failure possibilities.
- You end up jumping against the edge of the screen if you start too soon, little cloud platform doesn't appear fast enough.
- You wait long enough but lose the hammer bros lottery with a bad seqence of hammers.
- You wait too long and the height difference is too much to the last one.
It took me a while to figure out the sweet spot to jump, just before the hammer bros starts throwing, but just late enough for the cloud platform to slide into  the screen.

The green shell was a bit misleading, it seemed to just be there to get the mushroom at the beginning. It took a while to realize you were supposed to carry it along and ignore the mushroom power up.

I like the bomb puzzle and it looks great overall, however I suck at jumping on gears with Yoshi, especially when they move. The first part and where there are dry bones interfering give me a hard time. I made it past there twice, yet couldn't make the jump up at the arrow afterwards. I had to check in the editor if there was actually a platform there since you jump out of the screen. Queue more dieing in the beginning and I gave in to my 6 year old begging to play Splatoon lol. Damn it when they use the you're supposed to share argument against you :)
I wish Nintendo would release an editor for on PC, would be nice to build levels on my laptop with the mouse instead of my fingers. (I have kids, a stylus is never around for long :/)

Edit: I managed to finish your Dry Bones factory series. Great levels, great theme and each level has its own ideas. They get progressively more difficult though. I went through them backwards and it got easier. Still a lot of dying, but not too frustrating. No more jumping on moving gears please :)
The problem with that jump was that the arrow points straight up, while it seems you can only reach the upper platform and pipe if you jump towards the top right.

Weird, I don't have any comments on any levels either. Do you need to enable comments for levels?

Tried to give you 50 stars today, but your levels frustrated me too much, sorry lol! And I don't want to star levels I didn't beat.

I'd definitely tone down the difficulty. Then again, I made levels I beat on first try and only have a 3% success rate...

Y'all need to play my latest level some more!

Thanks for trying. It's that maker advantage I guess, a level I find pretty easy (Quirkafleeg) has the lowest clear rate 1.14%
I toned down haunted cathedral yet it still sits at only 6%. Only the last two were meant to be hard (Bowser's trial and Flight) I swear :)
My next level should be easier, should be more of a puzzle type situation and this time I'll keep it short. I suspect people simply run out of time in Puzzled mansion.

Yeah, I liked those and have starred them already a while ago. I'll keep playing your future levels! The ideas are good, but anxiety gives me chestpain, so hard levels usually aren't my thing.

I like puzzle type levels, don't try to put in hard platforming sections in a puzzle type platformer though, I feel like they don't mix well.

I'll play some of your levels I haven't played yet later.

I got stuck on your pogo jump level at the big thwomp.

That sequence is a bit problematic, it works better if you bail the first time, take the door back to retry and get there quickly. Let the little thwomp drop and spin jump after it to enter the tunnel to the big. Otherwise the timing of all the elements can be different making it much harder. Remember you can always fall down when hit to grab a mushroom and try again.
I tried it again and it's a lot harder now after not playing that course for a while... The sequence is to jump on, little bounces until close to the fire bars, big jump so the thwomp clears the fire bars while you always stay on the left of it, then little bounces to stay under the saw. At the top track time it right to switch to big bounces to clear the saw, back to little bounces under the next saw, then back to big bounces to either jump of the koopa for the 1up or stay on the thwomp and make for flag pole.

Hard levels get me stressed as well, yet I keep playing them :/ Luckily no chest pain but sometimes I have to stop for the safety of the gamepad lol.

Nope on both things. Use warp pipes for the first.