Adventure Time (S01E01)

Episode #001
'Slumber Party Panic'
Season 1, Episode 1

Princess Bubblegum's disastrous science experiment in a graveyard brings candy people back from the dead -- with a hunger for candy people's flesh. She and Finn proceed to rally the town into her castle to protect everyone under the guise of a massive slumber party while she works on a serum to get everything back to normal.

After the pilot episode established the characters and setting way back in '07 (here's a link to my video review for those who are interested), this opened up possibilities for a first official episode to explore different ideas beyond the early show's standard "Ice King kidnaps princesses and Finn and Jake have to save them" plot. Since this episode aired in 2010 when everything was all about zombies, it really should come as no surprise at all that they decided to go with that theme. That being said, it was a fun way to get the show started. Tons of characters are introduced here, the animation is great (and slightly "gory", in a very PG sense), and Finn's one-liners/puns are way too stupid not to be at least a little funny. Later in the series they would return to the zombie theme in a much more suspenseful and clever episode, but that doesn't take away from this one being pretty fun. And honestly, one of the better episodes of the first season.