War of the Heated Lake
Here's the death effect for SMB3 Hammer Bros from the community graphics pack.
Solid, if a little short and plain. Despite being a flotilla in a desert there's not much that distinguishes it as either instead of an airship with a different background and no pits, beyond the Dry Bones- it feels like either element could be emphasized some more through, uh, Sidesteppers, or Snifit-sprite-swap Cobrats, or Nat the Porcupine's Fire Snake / Blockhopper lua, or even essentially-harmless Bloopers between the ships? Not to assert the level should change too wildly, of course, and possibly the main project's desert world has its own reasonable bits (though most other desert-like enemies don't quite fit the airship lake here).
The part right before the first Hammer Bros is a little awkward, as placing the enemies directly on the ship sends them walking rightwards on a long flat section and thus easily scrolled offscreen if one waits. I guess they should be above the ship? There's a few glaring expanses of flat ground, really- a slope or a block on the front of the Bom-omb ship would at least provide a little hesitation there, and a block between the first two Thwomps would differentiate the two instead of being just a generous lead-in for the denser Thwomp part.
Each new level piece mostly gets discrete spacing, and while this keeps the level simple and easy enough for an early airship it also feels like the level just ends without exploring them much. The Bom-omb cannons and Thwomps only appear once, with the former not even getting anything particularly noticeable in its usage, while there's some basic iteration for Hammer Bros and Bill Blasters- if nothing else, putting a Bom-omb cannon at the lip of the final ship and a Thwomp right before the door feels like it gets a little more use and combination of the elements. Could also put another Bom-omb cannon on the ship introducing them right by the block, since one might need to double-back there.
Morton's earthquakes and asymmetric arena are nice for trying to introduce a little complication to the standard basics Koopaling fight, but the steps on the right side of the arena allows easily avoiding him hiding in his shell- more wooden slopes instead of steps would help Morton some more. The fight also might benefit from the boat still moving while inside it, or a Bill Blaster, or some other just-barely-further mechanical complication. Pushing just a little further describes what the whole level could use, really- this feedback has mostly ended up being what I'd do to give it more texture because there's not much to critique or highlight. It's there, it isn't too much, it has a little variety and some competence, and that's it.
Switch-it Plains
Oh, this sort of set-up. Hrm. The default SMW tracks are really muted compared to the constant (possibly too loud) switch sounds- custom samples of all of them might be reasonable. The enemies here feel quite sparing at the start, even if that's rather reasonable for the gimmick presented here in a first-world set-up. If nothing else, at least a few more Galoombas in the midpoint section would make sense.
These graphics are, uh. A little much, honestly. Curiously dense and thick textures for background elements, used much too close to one another- less is more when it comes to decoration, and there's kind of a lot packed into the main section here. Everything from flowers to hills to berries are a little too visually close to one another and static for rather plain sections. One egregious part:
If nothing else I kind of find the static berries uncanny and the hills much too filling. The majority of decorations disappearing in the second half would look better relatively-speaking if not for giant smiling static berry trees being the main decoration. The thin dirt terrain feel almost too thin, too, for some the irregular shapes- like, visual crinkle or something. Even if it's more generic, making parts like the cliff near the midpoint and around the pipe in the section following it thicker would look less off, I think.
The star room puts the complicated and dangerous part
after the star, which is surely self-evidently weird (even if it obviously takes not getting hit to spin-jump onto it). The midpoint just floats in the air- placing it on the ground or rotating the midpoint graphics for the level to place it on the wall would look better. The 1UP part in the same section (and the very final part of the level, really) feels far too difficult relative to the rest of the level due to being based on abusing an ambiguously-activated flaw inherent to the mechanic's implementation, and I'd rather have normal alternating sections (or more falling platforms) instead.
Also, the final section having no switch blocks in sight makes sense in terms of a mechanical break but looks odd in not having any visible blocks reacting to the sound of the switch.
The second half in general makes things quite hostile, really- the single blocks out-of-place show some teeth. Overall there's a lot of decent iteration on the switch-jump mechanic, since that's a driving focus for the level compared to e.g. that airship. The level is quite nice in that fashion, mechanically coherent and diligent enough for a presumably early level's introduced mechanic, though there are a lot more details I'd nitpick. It still spares a little room for moving layers and Parakoopas despite such an investigation, too.