IT'S FUNNY THAT THE VERY FIRST EPISODE OF "ADVENTURE TIME" CAN BE A HALLOWEEN EPISODE. But it is SO a Halloween episode.
Finn and Princess Bubblegum are in the graveyard conducting a science experiment with a serum that brings dead Candy People back to life. When the "Decorpsinator Serum" is used on the dead Mr. Cream Puff, it turns him into a zombie. Of course, he spills the serum over the other graves and creates a passle of zombies who will head to the Candy Kingdom because they crave the sugar the Candy People are made of. In order to protect them, PB summons all the Candy People into the castle's candy foyer under the pretense that they're to have a slumber party. PB explains to Finn that they can't tell them zombies are attacking because Candy People flip out and explode when they get scared. Meanwhile, the zombies are converging on the castle.
I think my favourite line in the show has to be when one of the zombies attacks Princess Bubblegum and says, "Gimme some sugar, baby!" This, of course, is a direct reference to Bruce Campbell's character Ash who says this in "ARMY OF DARKNESS". A funny thing is that this is the one and only episode that we ever see one of the Candy People (Starchy) flip out and explode when they're scared; it never happens again in the entire series so far. Another funny thing is that, amongst the zombies, you can see a "Zombie Finn"; no one ever notices this and nothing is ever said about it!