I'm glad you enjoyed it. The scripted events that take place in the level were very frustrating to get working consistently, but I'm pleased that I got those things to work 100% of the time.
The first Bowser Jr. fight had the issue of the player being able to run into the room and run back out before the door closed, which necessitated putting in a one way wall there. This was because the door absolutely needed to activate when the player crossed the threshold because if they walljumped against the left wall and activated the mechanism above while the mechanism was visible the enemies that make it work would be killed by the pow block. And of course the timed exit had to be just right so players didn't wait around wondering if the level was broken. I'm sure most of the time players kill Bowser Jr and the door opens almost immediately and gives the impression that I somehow made the door open by killing Bowser Jr. There was also a problem in an iteration where I just used a single spiny instead of a thwomp where Jr. would sometimes hit the the spiny when entering the arena and get stuck on the roof.
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The final version has a thwomp hit a pow block that kills a muncher supporting the red bill blasters on the left so that they hit a spring a bounce up to block the entrance. A pow block on a track starts moving and will eventually land in the path of the spiny that also starts spinning once you enter the room. That pow block knocks out the muncher holding back the right bill blasters so they are moved out of the way by conveyor belts.
The whole 2-phase 6-hit final boss fight went through several iterations as well. It was troublesome because the screen scrolls and, if the munchers are not on screen when the pow block activates, they won't be killed by it. So I needed a backup pow block mechanism in case that happened and I also needed it to trap the shell so that it would stop spawning and killing the bob-ombs that make the engine look like its exploding.
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The tall bill blaster near Jr fires flying bob-ombs that the piranha plants above ignite. You need at least 3 bob-omb hits to blast open the hard blocks on the right that prevent a spiny shell fired by the red blaster below from reaching the pow block on the right side. Once the pow block is hit, the munchers die 2 blasters in front of Jr. move along the conveyor belt and fill the space the hard blocks occupied. It's possible the screen is scrolled and the munchers keeping Jr. in place are not killed, which is why there is a pipe spawning infinite pow blocks that another shell can hit. Once those munchers die, a system of trampolines are released that shove Jr out into the stage as quickly as possible. I did this because it's possible for Jr. to kill himself with the shells he throws. When the munchers trapping Jr. die, the muncher supporting the pow blocks that come out of the pipe also dies, ensuring that future blocks fall into the hole the muncher was in and preventing future shells from hitting them. And of course, in case players don't get what to do or are having a really hard time, if they survive for 50 seconds a big bob-omb will come in and activate the 2nd phase of the fight automatically.
This is the design document I made for my first level: Boo's Plumbing Nightmare
I made it in Tiled. Much quicker than paper. Since then I haven't used it, though.
Well the thing is that teaching concepts isn't a 1-1 thing. It's how Nintendo makes every course, which became more and more the case with every new game. NSMBU, for example, introduces a new concept in every single level and rarely uses a concept as the theme of a level more than once. Whereas the first 1-1 needed to teach players concepts that were entirely new to gamers such as jumping on enemies, subsequent 1-1s were less concerned with that and introduced a new core mechanic as well. SMB3 introduces the super leaf. It didn't introduce slopes in 1-1 (though there are only 16 levels in the whole game that even have slopes), but SMW starts things off with a beach koopa sliding down a slope into your face. SMW introduces pipes thats shoot you like a cannon and the concepts of breaking blocks with spin jump and tossing shells straight up. NSMB introduces the mega mushroom, NSMBWii introduce the propeller mushroom and rolling hills, and NSMBU introduces the super acorn and focuses on moving semisolid platforms. The only hard rules seems to be that the levels are doable without dashing and the concepts introduced are fairly simple or ignorable by novice gamers.
