Adventure Time is one of my all-time favorite animated TV shows. It's about the adventures of a heroic human boy named Finn and his adoptive brother, a superpowered sapient dog named Jake, in a world a thousand years after an atomic war in which The Magic Returned, with disastrous consequences to Mankind (Finn may be the last, and is certainly one of the last surviving humans). Among the major recurring characters are Princess Bubblegum, a sapient humanoid being made of living candy biomass; Marceline the Vampire Queen, an immortal half-demon half-human vampire girl born before the war; and (Simon Petrikov, though he rarely remembers that name) the Ice King, who was a normal human Adventurer
It's had some great episodes, and unlike many shows of its type (Thundarr the Barbarian particularly comes to mind) has had real character development. Of particular relevance here is that the Ice King started as a fairly standard villain (his obsession was with capturing Princesses in the hopes that they would come to love him), quickly-revealed a pitiful and eventually a sympathetic side, and as of "Simon and Marcy," the episode immediately before this one, had essentially become an (annoying) friend of Finn and Jake. This was due largely to the fact that Marceline loves him for sacrificing his own sanity by using the Ice Crown to keep her (at that time a little girl) alive in the chaotic and dangerous conditions right after the Mushroom War.
This episode, "A Glitch Is A Glitch," was the worst episode of the show that I've ever seen, and here's why.
Someone throws a brick with a disk on it through Finn's window. Finn runs the contents of the disk and it first shows a raven-haired woman with long hair (who looks vaguely like Marceline) eating her own hair. The computer then glitches -- it was a dangeorus virus -- and then starts physically morphing. The virus has somehow accessed the fundamental nature of reality and is warping and deleting real objects.
It turns out that the Ice King, hearing Princess Bubblegum say "I wouldn't date you unless you were the last man in Ooo" mis-heard this as "I would date you if, and only if, you were the last man in Ooo." So he has decided to delete everything in the world save for himself and Bubblegum. This approach predictably fails: Bubblegum just beats him up, which however doesn't solve the more fundamental problem.
Finn and Jake travel to the fundamental level of reality, through the glitch, and fight the malevolent virus. They eventually get it to cough up all the reality it's been consuming and everything is set right again, save for the Ice King who finds himself splined into an object with a monster Jake accidentally created attacking him. Finn and Jake get a victory hug from Bubblegum. THE END.
I honestly don't know where to begin here.
The first thing is that the Ice King is behaving greatly and Bubblegum slightly Out Of Character. Bubblegum is OOC in that she would normally deal with a situation like this by doing something "science-y" -- she logically should have been the one making the portal for Finn and Jake to travel to the fundamental level of reality, if she could do it (and she's the most likely character in that universe to be able to do it.
As for the Ice King, it's been established throughout the series that the reason he's a (mostly) Harmless Villain is that he actually doesn't want to hurt anyone. His original personality, Simon Petrikov, is a profoundly good man, and he's kept the Ice Crown in rein for centuries. The Ice Crown wants to cover the world with eternal ice: any time that Simon wanted to destroy the world, all he would need to do is give the Crown what it wants. Instead, the Ice King has covered just one land with ice, where he reigns over penguins whom he loves like his pets and occasionally kidnaps some princesses to (mostly) just bore them with his insane fanfics and other social diversions, until they either escape or someone (both Finn and Marceline have played this role at times) rescues them. (Yes, I do know about the several times we know of before this that he did something worse, but it was never on the scale of mass murder. Or even murder).
To suddenly cast him as an Omnicidal Maniac is just plain wrong. That's not his character motivation.
There's another problem, which is that it's never been established that the Ice King has the power to do anything of this sort. His powers are all centered on cold and ice and derivations thereof (such as flying by summoning ice winds and using his prehensile beard as an airfoil). True, he's part of a Wizarding subculture that trades magic items (which is presumably how he got a Charm Person cursed ring to use on Old Lady Princess in one episode) but I don't see how he could get anything of a sufficient level of power to destroy the world. Aside from the one item he already has which has that power, the Ice Crown.
Dramatically, this totally went against the theme of the character arc they've been doing with the Ice King, namely that he's been becoming saner since Marceline's resumed her friendship with him. The Ice King commits his worst crimes out of loneliness, so the less lonely he is, the more nicely he behaves. That's been his character since the beginning. If he currently has an obsession, it's with making Fionna and Cake (the gender-flipped versions of Finn and Jake) become "really real" and in love with him; if he was going to do something wicked, it should have been pursuit of that obsession.
What I greatly fear is this:
Rebecca Sugar, one of the best writers/storyboarders for that show, did her last episode with "Simon and Marcy." She has always done the best epsiodes with the Ice King and Marceline the Vampire Queen, and it was largely her writing which established the characters of Simon Petrikov and Marceline Abadeer as people (rather than mere antagonists or allies).
Maybe they're doing a Take That to Rebecca Sugar. And if they are, I hope it doesn't ruin the series.
"A Glitch Is A Glitch" sucked. It really really really REALLY sucked. I hope this is an aberration, rather than some new and sucky direction for the whole series.