Righteous Quest is a game that appears on Adventure Time's official site on CartoonNetwork.com. It is currently the 3rd most played game on the website. It has a sequel called Righteous Quest 2, in which there are three standard levels, one boss battle, and two unlockable levels.
The first stage is through the Land of Ooo, when Princess Bubblegum asks the heroes to go and search for the Enchiridion while destroying gnomes with snowballs. The gnomes will fly high and shoot lightning at the player but are easy to take out. The player can use Jake's powers to reach high areas, fly, and if the player has collected 3 Jake Tokens, he or she can use Jake's powers to attack enemies.
In the second stage, Marceline has stolen the keys to the Tree Fort, and Finn and Jake have to fight Ninjas to recover it. The ninjas will either do a long kick or throw a ninja star at the player. Though they have great fighting skills, it only takes one hit to kill them. The player is introduced to Gumdrops, which he can use to jump really high. To get the keys, the player must get through two doors, one red and one blue. The only way to enter these doors is to find the two Key-pers hidden in the level. Once the player has found them, he or she must match the blue and red keys to the correct door to enter and recover the keys to the tree fort.
The final stage is in the Ice Kingdom, where the player must rescue Princess Bubblegum from the Ice King. The player must be careful, for the Ice Kingdom is slippery and the player could fall, making it harder to get around. The player has to also fight Snow Monsters and find two more gatekeepers to progress through the level. The snow monsters come in two different types: one that rolls into a ball to attack, and one that throws snowballs at Finn. It takes two hits to defeat each snow monster. After the player reaches Princess Bubblegum in an ice prison, the player must battle the Ice King.
The boss battle has three parts: In the first part, the Ice King will stay on the ground and shoot tiny ice bolts at Finn. He will also try to hit Finn with his long beard, which he must jump to avoid. Sometimes the Ice King will charge at Finn and move to the other side of the screen. After the player takes out some of the Ice King's health, he flies away to the next stage of the boss battle. The player must use Jake to reach the next zone. In this part, there are three ice platforms floating above and the Ice King is flying above them. The player must jump to one of the platforms and throw snowballs at the Ice King. Then the Ice King swoops down onto one of the platforms and shoots at Finn with frozen bolts. When most of his health is gone, he moves to the final area. Use Jake's ears to fly over the icy spikes to reach the next area. There are now six platforms floating and the Ice King is on the far left one. Use Jake to reach the first platform, then attack Ice King. The Ice King will fly up high and shoot huge frozen lightning bolts now which Finn must quickly dodge. Once the player defeat the Ice King, he is knocked out by his own crown and is defeated. Finn then gets embraced after Bubblegum is rescued.
If the player loses all of their lives, they will receive a game over. The game over screen is a closer up version of the image of Finn and Jake with a live lost, and it is on a blue background. There are words in yellow font that say 'Never give up!' above them, and how many points they earned. Depressing music plays in the background. In the second Righteous Quest game, the player receives the same game over screen, though it is closer up and the outline is thinner. The game over music is different in the second one. Instead of having the guitar music, it is one faint note.
- Finn: The main character who is controlled by the player. He can throw snowballs to attack.
- Jake: Jake is Finn's loyal dog who at certain points can fly or grow. He can also gain a special attack ability if one collects a coin with Jake's head on it.
- Princess Bubblegum: She first sends the heroes to recover the Enchiridion and later is captured by Ice King.
- Gnomes: These annoying characters shoot lightning, fly and can easily be killed.
- Marceline: She steals Finn and Jake's house keys, forcing the heroes to recover them. In the second stage she appears in the Tree Fort's window and hisses at Finn and Jake.
- Ninjas: Possibly summoned by Marceline, they will shoot ninja stars, do a long kick, and still require a single hit to kill.
- Ice King: He is the villain who kidnaps Princess Bubblegum and is the final boss of the game.
- Snow Monster: Ice King's minions. These monsters come in two varieties: a many armed snowball throwing golem and a rolling monster. These enemies require two hits to destroy.
- Key-pers: Key-pers can be found in two different colors: red and blue. The player must collect these humanoids to gain passage through locked doors.
- Gem: Collect to earn 15 points.
- 1-up: Gains an extra life.
- Heart: Replenishes health.
- Jake Icon: Will grant Jake his ultimate attack.
- Diamond: Gains 30 points.
- Sword Icon: Collect five for a prize at the end of each normal level.
- Purple Jewel: Gains 100 points and only appears after collecting 5 sword icons.
- Gumdrops: Makes Finn jump super high.
- Ice Booties: Causes permanent non-slipperiness in the boss battle.
- Unsheated: Collect a sword card (100 Points)
- Keyper Kompanion: Find one type of a key-per (100 Points)
- Master Swordsman: Collect all the sword cards in one game (200 Points)
- Ice Breaker: Defeat the Ice King (150 Points)
- Aggresive Adventurer: Defeat all enemies in the game (150 Points)
- Game Master: Get all badges for Righteous Quest (200 Points)
- If the player reaches the highest spot of the Ice Kingdom, they will see the two planets that appear in "Evicted!" when Jake sings the Home Song.
- Even though Lady Rainicorn and Princess Bubblegum appear on the start page, they do not appear in the game, only in the cut scenes.
- On the start page, Jake appears twice: once in the logo for the game, and again right behind Princess Bubblegum.
- Marceline also has purple skin instead of her usual pale blue-grey.
- A Ninja from the animated short appears in the start page.
- Jake can fly, even though he can't in the show. This could have been similar to the series' original pilot, "Jake-Less."
- Despite having been developed by a company from a Spanish-speaking country, its Spanish-translated version on the Argentinian Cartoon Network website ("Misión Honrada") has several typos (namely lack of diacritical marks or the starting exclamation mark in the message the player runs out of health) and even false friends. The Spanish Cartoon Network website hosts a version with a different name ("En Busca de la Justicia") in which most of those mistakes have been corrected, but the language style isn't close to the one used in the European Spanish series dub.