Card Wars is a card game that Finn and Jake play in the episode "Card Wars." The rules to the game are "super complicated," and it took Jake two hours to explain the basics of them to Finn. It has also been made into an app, the wiki for which can be found here. There is also a real card game version of Card Wars.
When the game starts, two players get approximately 10-20 cards. There are two stages to a turn: a floop stage and a battle stage. A player may take any building card and floop it (turn it to the left) to appear as holograms on the board. Buildings have special effects which can aid the player using them. There are only two known elements of the game, which are corn and learning. Corn cards happen to be powered by corn fields, which are given to the player at the start of the game. Learning cards are powered by intelligence, so a player could send someone to learn, and in turn, that person will receive power.
There are three segments of the players' land: the land, a mud pit, and an empty field. A player may select a creature and either activate it (turn it to the right) to make it attack one or more of the other player's creatures, or floop it to make it use its special ability. Also, at the lower right corner of each creature card there are two numbers with a forward slash representing that specific card's stats. A player can also use activation to make a creature learn. Before beginning a turn, a player must discard a card from his or her hand and pick up another card from his or her deck. The player that loses all of his or her creatures and their buildings at the end of his or her turn first loses the game.
There are many cards shown in the game. The known cards are:
"Study" is used to command the Ancient Scholar to go to the Schoolhouse so it can discover new powers such as "Raise the Dead."
"Raise the Dead" is used to bring a dead ally back to life, but to use it, one needs to study it first to unlock it.
Finn used the Study ability in order to learn Raise the Dead, which he then used to bring back his Pig card. It was one of the only known cards on Finn's base, and was around the Cool Dog most of the time. He looks like a wizard who wears a purple cloak with a hood.
Can shoot multiple corn-arrows per attack phase, each of which are capable of destroying a building.
Jake summons Archer Dan on the last turn of the game and destroys all of Finn's buildings at once.
It is used for the creature to gain +3 defense.
This card was flooped at the beginning of the game but is merely an aesthetic part of the episode and is not used.
Cave of Solitude
It is used for the creature to gain +5 attack and +5 defense for each of the player's empty landscapes.
Finn sends his Pig here to rest up. Jake attempts to attack the Pig, but is unable to affect him. Eventually, he uses Volcano to destroy the Cave of Solitude along with the Pig.
The Cerebal Bloodstorm lets you choose your opponent's creatures and destory it equal to the creature's attack.
Jake uses Silo of Truth to take this card from Finn and uses it on his first attack phase, but because Finn wasn't attacking, Cerebral Bloodstorm only did damage to Jake's troops.
When the player flooped the Cool Dog, the Cool Dog's opposing creature cannot use the creature's floop ability.
Cool Dog's powers are unknown because he is never used by Finn.
One of Jake's landscapes in the episode, the others are Useless Swamp. The landscape is also seen at the game.
Jake uses the Cornfield to power his Husker Knights and give his Immortal Maize Walker triple damage. Finn uses his Pig to eat the Cornfield, defeating Jake's army twice.
Field of Nightmares
In the episode, Jake the dog uses it to scare Finn's pig to death.
Jake used this card in conjunction with his Legion of Earlings, though it is not clear what effect it had.
Can take control of five of the opponent's creatures at once.
Jake summons this creature on the last turn of the game. It takes control of all of Finn's creatures at once.
In the game, Husker Knights are only knights that has 2 defense and 6 attack. In the episode, it is used by Jake to attack Finn's kingdom but died.
Jake attempts to attack Finn with these creatures twice, but they are defeated by the Pig eating Jake's Cornfield (their source of power) both times.
Immortal Maize Walker
In the game, it is a special and powerful creature that has 36 defense and 11 attack. While in the episode, Jake summons the creature but Finn's Spirit Tower makes the creature goes to Finn's side.
This card was used by Jake to attack Finn, but it was stolen by Finn's Spirit Tower. Jake later took it back by use of his Field Reaper. When powered up by corn, its features become more jagged and lightning-like sparks shoot off its body.
Legion of Earlings
It is able to scare other creatures to death.
Jake attempts to kill Finn's Pig by scaring it to death, but the Pig is sleeping in the Cave of Solitude and is unaffected.
Eat: Pig eats the corn off of an opponent's land. Punch: A simple, physical attack.
Finn used this card to eat Jake's Cornfield, which defeated Jake's Husker Knights. Later, Finn attacks Jake's Wandering Bald Man with the Pig in simple combat.
Allows player to reconstitute all of their land.
Jake uses this card after using Volcano, in order to reconstitute all of the land that was destroyed previously, reviving his Husker Knights in the process.
One of Jake's landmarks in his field.
This card was not used for attacking.
It allows Ancient Scholar to use his Study ability. It's unaffected by cards such as "Volcano".
Finn sends his Ancient Scholar here for one round to study the "Raise the Dead" ability.
Silo of Truth
Reveals the target opponent's hand and allows the user to take one card and add it to their own hand.
Jake used this card on his first turn in order to look at Finn's hand. Jake takes Finn's Cerebral Bloodstorm card with it.
Can possess an attacking enemy and turn it over to the player's control.
When Jake attempted to attack Finn with his Immortal Maize Walker, the Spirit Tower shined a beam of light onto the creature and turned control of it over to Finn.
Teleports a player's own creature to another place on the board.
Jake attempted to use this card on Finn's Pig in order to get it out of the Cave of Solitude, but it only works on the player's own creatures.
Immortal Maize Walkers can walk on this land.
The Immortal Maize Walker was hiding underneath this land. Later, after Pig and Wandering Bald Man fight here, Pig is unable to leave because it is a mud landscape.
Spews lava to destroy both land and creatures for all players.
This card was activated by Jake to kill Finn's Pig. It destroyed all of Jake's land, but he used Reclaim Landscape to reconstitute all of it.
Wandering Bald Man
Slap: A weak, physical attack.
Wandering Bald Man wanders around in the Useless Swamp until Finn attacks it with Pig. They both do minor amounts of damage to each other, but Pig wins the fight in the end.
The board of the game shows holographic projections of the played cards. The back of the cards are red in color with a white border. The cards have the letters, "C W," which stands for Card Wars, and there are flames in the background.
There is also a real-life version available at various retailers and online shops. A description can be found here.
There is a "Card Wars" game now available on iTunes for iOS and Google Play for Android which costs $3.99. It has also been released as a board game for aproximately $20, with two different versions: Finn vs Jake, BMO vs Lady Rainicorn, and Princess Bubblegum vs Lumpy Space Princess.
The game is a parody of various trading card games.
For example, "Flooping" (to turn a card sideways) is a reference to "tapping" in Magic: The Gathering.
Tapping was patented by Richard Garfield, creator of the modern TCG, in 1993. (US patent # 5662332)
Card Wars bears a similarity to the Yu-Gi-Oh! and to the Cardfight!! Vanguard trading card game.