>>86319706While I agree with everything everyone has said about lurking horrors and not showing the monsters, those are two really bad examples to use because those are comedies. Bill is supposed to be funny and likable and while I guess the Lich is the most serious character in Adventure Time AT is still a silly show so there's only so many times he can show up before some goofy shit happens around him.
With Aku, hmm, even though Samurai Jack wasn't a comedy it still seems cartoonier than OTGW in a weird way.
Another thing to consider too is brevity. OTGW was a mini-series. One huge problem with villains is they have to keep losing and eventually, they don't seem scary anymore. The Beast is barely shown and not clearly. He doesn't have to keep getting beaten by the good guys, it doesn't even feel like a clear cut good guys vs. bad guys story, the Beast is more a force or concept.
Actually he only "loses" at the end, and you know what, it's strange. Because he actually does stop being scary at that point, but it's I think intentional, and effective? He's almost pitable at that moment. And...
He is a symbol and represents things like death, depression, giving up. But it's sort of like the fear of the dark. Wirt realizes it only has as much power over you as you give it, because of fear. After he threatens to blow out the lantern, there's this dismissive look he gives, and you know he's overcome that, as the last trial. And now he can move on.