Adventure Time: The War Chronicles is a spin-off series premiered on Martin Luther King Day 2012. The season began with the half-hour long episode "Finn & Fionna" and is ongoing.
The series was highlighted by several arrivals, departures, changes and revelations.
- The storylines gave way to darker, more grim storylines.
- Jake and Cake's roles have been downplayed to focus on Finn, Fionna and Princess Bubblegum, who became the three core characters of the series.
- The music, which was usually synthesizer music that sounded 16-bit at times, gave way to new music composed and orchestrated by John Williams and London Symphony Orchestra. Music by Akira Ifikube, James Horner, and Danny Elfman is also featured.
- Fionna and Cake joined the main cast in "Finn & Fionna".
- Japanese kaiju (IE Godzilla) were introduced in "Destruction & Despair".
- The Fourth World War between the Candy and Nut Kingdoms began in "Shock & Awe".
- Finn and PB's status as a couple is cemented.
- As mentioned previously, the storylines became darker.
- The theme song was changed (read this article to learn more).
- Towards the end of the season, PB decides to join Finn & Fionna on the frontlines. However, since her skirt would hamper her mobility, she changes outfits. It is basically a pink version of Finn's outfit. Her hair is up in a ponytail, and her tiara is gone. She is still seen in her dress in between battles and during official business.
- Fionna is Finn's long-lost twin sister (basically retconning Ice King's fanfiction).
- All is revealed about the Great Mushroom War (under the new name World War III),
- Finn & Fionna - Finn meets Fionna as The Lich advances on the Candy Kingdom.
- Trip To The Moon - Trudy drafts Finn and Fionna for a mission to the moon to fight an alien race.
- Shock & Awe - World War IV begins!
- Light My Fire - Flame Princess incites a rebellion to overthrow the Fire King.
- Good Samaritan - When Princess Bubblegum gets struck by lightning, Finn stays home to take care of her. Meanwhile, the Nut Kingdom advances on a strategic position.
- Highway to Hell - The Evil Kingdom attacks Fire Kingdom convoys along Interstate 5, earning the attention of the Candy Kingdom.