But I Have a Receipt

Synopsis
Mordecai and Rigby try to return a mediocre role-playing board game (The Realm of Darthon) to a grumpy store manager. But when the manager refuses to give a refund, the duo try to retaliate by pointing out the board game's imperfections to oncoming customers. After driving out his last customer, the enraged store manager traps Mordecai and Rigby in the game and it's up to them to escape and get their refund.

Plot
Mordecai and Rigby buy a game, The Realm Of Darthon, but find it mediocre. When they come to the store where they got the game, they attempt to return it, but the manager at the store explains that they cannot return the product if it is opened, and they won’t get their refund, even though the duo has a receipt. This angers them further, so they decide to sabotage the manager’s business until they get their money back. They show up at the store again wearing amateur costumes and creative cars from the game and explaining how lousy and difficult the game is. Every time they mess up his campaign, the manager lowers the price down until it’s completely free with purchase of gum, even still managing to sabotage it.

The manager could not take Mordecai and Rigby’s sabotaging no longer, and uses his power from the game to actually send them inside it, making the costumes they’re wearing turn real. They still refuse defeat until they get a refund, so they are pitted against enemies the manager throws at them. When Mordecai and Rigby manage to escape the enemies, they find an army of enemies and they fight. Rigby manages to use his power to bring Benson, Pops, and Skips inside the game world as the characters they were playing as on the night they were playing the game.

The manager sees that their teamwork is too powerful, and sends Skips, Benson, and Pops away. The manager appears as the game’s ultimate player, Darthon, and keeps using his power to beat Mordecai and Rigby. As he was about to get them eaten by a giant monster, they discover that they can control the game too using their imagination. This causes them to have a battle of wits with the manager, and Mordecai draws a sword that is immune to all rule changes. He stabs the manager with the sword, and they reappear in the real world, with Mordecai and Rigby back in their amateur costumes, and the sword the manager got stabbed with became a ruler.

As they beat him fair and square, the manager gives them their money back, but gets gravely wounded by the ruler stabbed in his chest, despite Mordecai and Rigby’s attempts to give him help. They are then encountered by Pops, Benson, and Skips, who explain that one second they were in the armor closet then they appear in a shoe store. It is revealed that the money Mordecai and Rigby risked their lives for was $7, which greatly angers Benson. However, Mordecai and Rigby decide to spend their refund money on another game, which further confuses their friends.