I'd have to say my least favorite episode is "Red's Sea Monster" it's really frustrating because the fraggles refuse to believe red saw a sea monster when literally the entire rock is populated by fantastical things, INCLUDING THEMSELVES! so already the entire basis for the plot is flawed, then towards the end of the episode the audience is supposed to be pitted against red by this really annoying line "she dug herself in and now she'll have to dig herself out" it sickens me that gobo has the audacity to say that when he's the one who composed the cruel prank against red and drove her to camping out near the lake, it's like a worse version of "Mokey's Funeral" where the characters are so uncharacteristically mean-spirited for no reason other than plot contrivance, I love fraggle rock with all my heart and I was fine with this episode as a child but through an adult lens, it really frustrates me how everyone treats red in this episode, there's a lesson there that you shouldn't put so much emphasis on pride and attention but it's bogged down by everyone being so hurtful to her, besides that, Marlon was such an underutilized antagonist, the guy has a history of being the rock's creep but he doesn't really do anything in this episode besides set up a trap, I'm not saying he should've outright murdered the lily creature, I just wish the episode gave him something more villainous to do rather than sit around, fantasize about power and set up a trap that immediately gets immobilized, over all, a very frustrating poor episode, I'd have to give it a 5/10 on the positive side, fraggle rock is as per usual gorgeous to look at, red's song is beautifully sentimental as well as nostalgic and lastly the lily creature has a very captivating design and the puppetry is masterful, these are just my thoughts on the episode I consider the worst.
P.S. Red's Blue Dragon has many of the same issues but it's less extreme