These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Horror: In "Marooned", Red and Boober are trapped in a cave-in and running out of air. They both quickly recognize the symptoms of this. Suddenly, living underground doesn't seem quite so charming and carefree...
Magnum Opus: Combining music, puppetry, ethos, on an international level from the very start.
Wangst: Gobo occasionally falls into this, mostly based on his status of de-facto leader of the gang. As early as the first season, he spends most of the Invisible Garboil episode in the depths of a Heroic BSOD!
This is even parodied in the second-season episode "Wembley and the Great Race", where Wembley has a Dream Sequence in which Gobo goes completely to pieces over losing a race.