VG Thought

World 1: https://www.youtube.com/watch?v=rtjXr_QytVg
World 2: https://www.youtube.com/watch?v=ZgL-9YFhqFU
World 3: https://www.youtube.com/watch?v=2HgyvPnN3Ww
World 4: https://www.youtube.com/watch?v=t1sv-2OoWLs

World 2:

2-1
First half is wide open, lots of horizontal space. Second half is tight platforming, cover vertical space (scale a wall). The green ! panel only appears at the very end, but it complements the yellow moving platforms as a timed challenge.

2-2
All about the green ! panels. They move at Mario's running speed, so you can't outrun them, but if you go too quickly, you might not have time to readjust your course if the panel flips some way you don't expect. The challenge is to clear jumps before the panels recede.

Two coin snakes around the midpoint. The latter one is activated by a powerup hidden earlier in the stage and leads you to a hidden star coin.

You'll need Super Mario to get the third star coin. It might not be obvious that Super Mario can get it, though.

The green ! panels lay out a pretty tight path, so I guess it figures that two of the star coins are hidden rather than placed on that path.

2-3
You need either a propeller block or raccoon tail to clear this because it's impossible to get to Peach without either. Can be cleared with just the raccoon tail, though.

Lots of optional stuff on each platform. It might seem like the level is just about the propeller block, but you'll need the raccoon tail on each giant sprite platform to get everything.

2-4
In Super Mario Galaxy 2, these would flip only when you did a spin.

The third verse of flipswitch platforms is the interesting one, since you can control how enemies spawn. The fourth verse is longer and has strict timing challenges with its spinning spike bars, but the third verse is the more interesting challenge because you can influence enemy behavior.

That third verse shows how games can allow for different playstyles even with a limited space and simple elements. The fourth verse is the squeeze.

2-Doomship
Rocky wrench appears once. The flame jets disappear in the second half of the stage.

The bullet bills get variation in space. The first volley is against a tightrope, where Mario effectively occupies 2D space. The second volley is on a ship, where Mario can run around in 3D. For the third volley, Mario can use 3D space, but the bullet bills have raccoon tails, so they themselves take up more 3D space than they did before. The first challenge is simple (you only have 2D space) and strict (not much space to avoid bullet bills). The second challenge is complex (you can roam 3D space) and free (this gives you more room to dodge bullet bills). The third challenge is complex (you can roam 3D space) and strict (bullet bills occupy a larger portion of that space). It's about how much space it's possible to occupy versus how much space bullet bills will occupy.

World 3:

3-1

Opens with a wide open area. A number of things to discover and challenges to overcome at your own pace, if at all. Skip 'em if you want! Enemies track you underneath the sand in any direction (sandmaarghs). The only way to get to the rest of the level is to take a cannon.

Scaling the tower, you'll encounter thwomps and wallops. Thwomps crash down in one line as you approach. Wallops walk side to side along one line and jump to block your advance. Thwomps and wallops complement each other. They both strike vertically depending on your position. Neither hurts you unless you're under them. Tricking them is helpful.

The "bridge" of the level is a series of blocks that move independent from Mario's movements, which contrasts well with the thwomps and wallops--blocks that move based on Mario's own movements.

The level ends with another area with optional content.

3-2

A lot of the level feels 2D because the space will only be three blocks wide. When three cheep cheeps swim side by side, it feels like a 2D challenge. But use your fireballs, and suddenly 3D space is relevant.

3-3

Suspension--you'll need to come in with a raccoon tail to get the first star coin.

Running in a straight line conquers a good deal of the level. There are two interesting parts: the red coin part, which keeps you over a bed of donut blocks in order to get every red coin, and the layup to the third star coin, which asks for precise jumps off of single donut blocks.

3-4

On the second fuzzy tightrope, you can jump up into the swinging ball. Neat!

Tightropes make it easy to compare alternate paths. (Sonic Lost World Sea Bottom Segue???) One neat challenge has you track where you are along perpendicular tightropes.

3-5

Para-biddybuds move on different axes from cookie platforms, complementing them well. In the second half, cookie platforms expand in width to offer challenges across the same axes as para-biddybuds.

3-Doomship

Run past moving spike bars. It's cool when donut blocks are sat next to them, since you activate a donut block's timer yourself--you have to compare that timer against the spike bar timer that runs on its own. Bob-ombs and spike ball cannons will track the player.

x-y: Game is bad, play 3D World instead

Aw man, I love 3D Land. 3D World is fun but too diverse for my tastes.

World 4:

4-1

Platforming with bouncy mushroom platforms. There are several enemy chains for 1ups (mostly biddybuds). Both halves of the stage start horizontal and go vertical. The looping tree path allows a single path to loop around itself.

4-2

Cramped spaces. Small rooms are stacked on top of each other. Goomba stacks fit well, since they don't take up much horizontal space. A lot of mushroom platforms with a few ! blocks thrown in. The small space allows for nooks and crannies hidden just out of view/behind something.

4-3

Spinning blocks. The first half puts in a few at a time and even mixes in a music note block and a ! block. The second half puts a bunch of spinning blocks right next to each other. The first half contrasts spinning blocks against other kinds of blocks, while the second half asks the player to manage the timer of multiple spinning blocks at once.

4-4

Tension between boos and appearing platforms. You can't move too quickly, or else you won't see where you're going. However, this gives boos time to gain on you. The star coin over a pit is actually on an appearing platform, but unlike every other platform in the stage, it will only appear once you stand on it. (The others appear once you get close to them.) The second half opens up with several branches to try and a large platform with lots of boos to catch you. Then it moves on to a race away from one huge boo. One open part with lots of small enemies and one super straightforward part with one big enemy.

4-5

The whole level features multiple uncurling platforms working together at the same time. The first half has more vertical climbs and the second half has long, winding horizontal paths. Boomerang bros show up on wide, safe platforms.

4-Doomship

Flipswitch platforms while enemies throw stuff at you. Rocky wrenches come and go, but the boomerang bros hop around to bug you consistently, and their projectiles even loop back around (sticking around longer than wrenches). Top it off with a boss that also throws boomerangs. You can jump on any projectile in this level to kill it. There's a hidden top path with a shitton of coins (but then you miss the middle star coin!). One star coin at the start is resting above a flipswitch platform; its brother coin later on actually moves with the flipswitch platform, going under it if it's in the wrong orientation.

5-1

New powerup introduced 5 worlds in!
First half is a walk around a mountain facing a variety of enemies. Each section has its own enemies, and no enemies are repeated. Constant variety!
Second half sticks you in an arena. Enemies can hang around for multiple phases if you let them survive, so it's in your best interest to be proactive. Spike balls will eventually kill them, though.

5-2

First half starts with slowly growing rooms, introducing spinies and spike bars one by one. Very carefully paced.
Second half introduces bottomless pit challenges alongside spinies with a long spikebar challenge in between.
You can kill spinies with rocks!

5-3

Single moving yellow platforms with spinning spike bars, then double yellow platforms with different enemies introduced.
Flophopper makes use of contrary motion by passing right underneath the three boxes.
The first yellow platform segment asks you to manage just one platform. The second one asks you to manage two platforms and enemies. And the third one asks you to manage platforming alongside moving platforms so that you keep up.
The stage progresses by variety of counterpoint.

5-4

Reminds me of Valley of Bowser 1.
First half focuses on hiding to avoid enemies. There's tons of hidden passages! The second half layers enemies together, and the level design is more open.

5-5

First half has a moving cloud up next to a safe platform. Second half has a ton of empty space. It's really hard to gauge distance in the second half.

5-Castle

First half has single lines of moving platforms that sink. Challenge is to get your shit done before it sinks.
Second half blocks you with thwomps (narrower than the first half), then opens up to dodge fireballs from Bowser (freer than the first half).
Bowser himself unleashes a few attacks and then lets you pass for each of his rounds.

World 6:

6-1

In the first half, cheep-cheeps and porcupuffers approach the bridge from a distance. They approach the player from the side. Then, goombas and biddybuds approach head on. Take note of how enemy introduction is paced (you only get the ground enemies after a few iterations of flying enemies). The final challenge is on a tightrope, making timing tighter.

A secret swimming area offers more freedom of movement than the normal bridge level does, which is almost 2D.

The second half keeps timing tight with more tightropes and longer strings of porcupuffers. Note that there are no ground enemies in the second half.

6-2

A series of one-room challenges with pokeys. First two rooms have spike traps, third room is a bridge segment (it's just an elevator), and the last room changes things up by having to study how the rising platforms work. This last room takes having to study the floor and adds the complexity that different parts of the floor will act in slightly different ways, since different parts of the floor will rise higher.

The second half takes elements from the first half (elevators, spike beds) and introduces bottomless bits between them. This stresses your fine-tuned knowledge of them. For example, it's not good enough just to know that spike beds are bad. You now have to know when they're bad.

6-3

Every ! block always goes to the same room, but each time you enter the hub room, the coins advance a space. You get a couple different challenges (moving piano key platforms, crazy box maze), but only the shifting wall challenge gets much time.

In the second half, you need to time yourself against shifting books so Mario doesn't fall in a pit balanced with getting away from chasing boos. The last challenge puts a twist on this by forcing you to let a big boo chase Mario.

6-4

Blocks that appear in time with the music. It fools around with enemies on the side, but only one wallop gets in the way of a disappearing platform at the end.

Second half layers them with other challenges (moving spike bars) and varies the shapes of disappearing blocks (curved, sloped). When challenges are placed over top of a disappearing block challenge, they're all static timers--you can't influence how spike bars move. Note that you can influence how that wallop at the end of the first half moves, though.

6-5

The first half has some timing challenges versus goombas and moving mushroom platforms. Make sure to pause in front of the third mushroom platform to show how far it moves side to side. Then, there's a mushroom platform that you need to follow along a track. In the former part, you can rely on safe ground and move out to dangerous moving parts at will. In the latter part, you have to follow the mushroom platform all the way; it forces the pace that you approach challenges.

The second half has a similar moving mushroom platform part, but with less safe space versus goomba space. The level caps off with another approach-at-your-own-pace mushroom challenge.

6-Doomship

A sequence of spiked pillars. Starts out by moving between the background and foreground, but quickly switches to vertical and side to side. Two bomb-throwing rocky wrenches make things hard.