This is an amazing episode thus far (I'm somewhere at the start of world 8 as of now), really nice usage of the different playables in various levels, really great design all around (as was to be expected), just really great. My only concern is that, while most of the episode is hard in the good way (challenging, not cheap and annoying), a couple of levels do feel like they're a little too much. In particular the sky pop level is a bit too much bullet hell for me (especially considering it's not in one of the last couple of worlds) and getting the hammer suits from the toad house is nigh mandatory if you want to stand a chance in it. The (first?) bossfight against Wario and Waluigi is pretty cool, but I feel like it would benefit from giving a mushroom or something about halfway through the battle since it's not a very short fight and one where you will probably get hit a couple of times. Other than that, it seems like it's very balanced difficulty-wise, with a few difficulty spikes that aren't too major.
One bigger thing that really did annoy me was the General Toad boss fight and the level where you play as him. The boss fight felt very cheap due to the way Toad throws bombs (basically it's hard as fuck for me not to hit myself) and in the first part of the fight, the whole stage gets blown up too fast. It would benefit from either removing the chasing enemy spawn or making parts of the stage non-breakable at the very least. As for the level with General Toad, playing with Link feels quite unnatural and the level design is rather difficult an sich (especially with the boos, which can neither be killed nor be spin jumped on), making the level an absolute pain to complete. If this thing could be made more playable I'd love it because fuck Link, honestly.
Oh yeah, the first Waluigi fight is glitchy by the way, you might wanna ensure the events occur as planned all the time because I got stuck twice.
Dunno if you will do anything with this since you seem to have stopped designing, but uh, if you wanna make your magnum opus as good as possible it might be worth it 0: