My review of The Forbidden 改造:
For some reason, I have trouble deciding how to begin this review. I guess it's because one of your first design choices makes me want to go on a tangent about how its representative of something that is never good design: having to catch the key in midair before it falls down a bottomless pit. Don't get me wrong; this would be pretty clever if it were used to get a secret, but since it's mandatory for the player to do it to progress (three separate times, no less!), it, and anything else like this that renders the level impossible to beat if the player fails, just gets annoying really quickly. Plus, if the player gets Game Over on that level, he/she can just skip it, and that's the only way I can see the player not having enough stars to get past the first finale level (by the way, why do you even have that star-locked door there in the first place? You made it so that the player can't go back from that point, so if the player somehow didn't get all the stars, the only way to do so would be to either start the entire episode over again or cheat).
By the way, when the player beats Begins, a path is opened that leads straight to Mouser Bros., so I guess that's another way the player can make it to the finale without all the stars, but you could just have the path connect to the left side of Toadsworth's House, then set its Level Exits to "0 - None"; that way, the player wouldn't be able to skip straight to Mouser Bros. Speaking of Toadsworth's House, you used the wrong tiles for the bottom of the island; when connecting the bottom of island to the water, you should use the tiles with water below them, not land:

Looks much better, don't you think?
Also, speaking of Begins, another design choice you shouldn't use is starting the player in a position that requires the player to react quickly or get killed. Plus, there's no indication that the player has to move to the right until after the floor shows up, and by then, it's too late for the player to do anything. You should make all your levels so that first-time players have enough time to react to the level's obstacles.
The Key is Key, the third level, brings up yet another bad design choice: unindicated invisible blocks. Whether they're set as a trap or hide a secret, invisible blocks should always have some indication that they're there, like being surrounded by coins or something. Also, you're aware that keys and other carryable, non-enemy NPCs will fall through block tiles when placed within block tiles, right? I ask because you placed two keys at the beginning, but only one is required (same goes for its duplicate section in the finale).
Dodge-Bomb is just annoying. For the first section, it's nearly impossible to avoid the bombs without getting hit due to their frequency and various delays. The second section sets the player just above a poison mushroom, so if the player enters while little (something that is highly likely to happen), he/she gets killed and has to go through the level again. Plus, the player can bypass the poison mushroom without taking damage by abusing power-up invincibility, so if that was meant as a power-up filter to prevent the player from being able to take the explosion of the last bomb, you failed. Either way, it's boring having to wait for the last bomb to explode.
Boom Boom's Spikey [should be "spiky," by the way] Battle was actually pretty fun. Although it was annoying having to wait for the line-rider to move back down to where Boom-Boom was (and waiting = boring = not fun), I liked the idea of having to kill the Boom-Boom without letting the line-rider get away from the player. However, I encountered a glitch that causes the Boom-Boom to die prematurely:
Apparently, when a Boom-Boom is stomped and lands on a moving layer or a line-rider, it won't get pushed by non-moving blocks but will still get crushed if it's moved inside said blocks (the line-rider is moving right in this screenshot). The arena would have to be redesigned to prevent Boom-Boom from jumping off-screen and to prevent this bug from happening on the walls that would be added to prevent Boom-Boom from jumping off-screen, but to prevent this one instance of the bug, I recommend moving the lines-that-move-the-line-rider-up-at-that-area one unit to the left.

Hop to it! was oddly easy for an episode that's supposed to be "改造," though I wasn't able to enter the door when time was stopped for some reason. Just so you know, as long as the player is above the Thwomps, they won't drop down; it doesn't matter whether time is stopped or not.
Deja Vu is just padding (there isn't enough done to differentiate it from the first level), and since it also has a "hey, I couldn't get this to work right, so I'm warning you instead of fixing it" bug, this level should be removed.
MUST PROCEED IN A HIGH VELOCITY is also really annoying. Not only does the player have to jump through that really small, really long, and really empty staircase, but right after that, the player also has to time a running-jump perfectly so that, when the P-Switch runs out, he/she can jump over the wall without the moving layer speeding away. This is extremely difficult to do and requires the player to be lucky rather than skillful. I recommend removing that wall and adding some hazards around the staircase. Also, what was the point of Section 2? There wasn't anything there besides the Koopa Klown Kar and the star; it would be better if you just put the star at the end of Section 1.
The Lemmy and Ludwig fight, although simple and designed against the bosses, was effective since the player has to deal with more than just 1 type of pre-programmed AI at once. The only issue I have with it is that, once the bosses are defeated, the player just has to wait there for like, half a minute before the bombs are generated to destroy the blocks blocking the pipes (and that the bombs are generated without warning, so if the player is standing where the bombs explode, he/she won't have any time to react to them and will have to go through the level again). I recommend removing the bomb generators, putting Lemmy and Ludwig on a layer, placing the star in Section 1 and on a hidden layer, and setting Lemmy and Ludwig to trigger an event that reveals the star in their "No More Objects in Layer" slot.
As for Mouser Bros., the concept was neat, but you had too many bomb-able blocks for the floor to make it any challenging (remember that the player can grab bombs in midair, too). I recommend only having two rows of bomb-able blocks, like in Legend of the Blob Bros 2. Also, why do the boss fights get
easier as the episode goes on? Did I accidentally go through the episode backward or something?
Regarding the finale, your attempted wordplay doesn't work since you have a Tetris remix playing instead of The Final Countdown. Also, although you know the concept for a good final level (test what the player has learned), that isn't an excuse to make a gauntlet of basically-the-same-level-designs-the-player-just-went-through; that's just padding. You're supposed to blend the episode's previous gimmicks together to make something new, not stitch together previous levels' sections into one big level. Plus, the coin staircase in Section 3 can be skipped since the player is able to collect some of the coins that form the wall before hitting the P-Switch. As for the boss rush at the end, the Birdo/Mouser and Boom-Boom fights are both easier than their previous counterparts due to the fact that the player can just kill Birdo with Mouser's bombs to activate the door and the fact that the player can jump to reset the doughnut blocks as well as just jump on Boom-Boom when he walks by. Both of those fights should be remade or removed. As for the Lemmy/Ludwig fight, that was surprisingly difficult, but just like the Birdo/Mouser fight before it, only one has to be defeated for the player to progress, and that seems unintentional.
By the way, when the player beats that level and is sent to the second "half" of the finale, the road to Congratulations!!! is revealed; to prevent this, select the level icon for "FINALE 2/2" and set its Bottom Level Exit to "7 - Star Exit." As for FINALE 2/2 itself, it's just a generic SMB3 Bowser fight except there are more than four rows of SMB3 Bowser Bricks. Of course, that doesn't matter since the player can just become Link, shield Bowser's flames, and stab Bowser to death, upholding my claim that the bosses get easier as the episode progresses. Lastly, although I know it's supposed to be a joke, the SMB1 Bowser fight in Congratulations!!! is just boring since the player just has to wait for the conveyor belt to push Bowser into the lava while avoiding the occasional flame.
In conclusion:
This episode is plagued with unindicated invisible blocks, an inconsistent difficulty curve, and the repeated use of basically-the-same-sections, as well as a few other miscellaneous design flaws. I know this is supposed to be "改造," but if the episode is too difficult (or just really annoying), it isn't fun to play.
P.S. As for the secret level, although it may be clever in theory, I don't see any way its execution can be anything except unintuitive or painfully obvious; nobody would think that the solution is to actually cheat.