When Lord Hater's attempt to send Wander to his prison dimension backfires when he ends up there as well, he winds up clashing with the other inmates who despise him. Lord Hater struggles to be Wander's buddy to survive while adapting to everything he does.
On Lord Hater's ship, Wander has been captured and is forced to go to the Pit of Perpetual Pain. Hater explains it is a portal to a prison dimension where he banished those he has detested and intends to banish Wander there as well. At the last minute though, Sylvia then comes to his rescue, attacking all the Watchdogs that come at her. She then throws one of them at Peepers, causing his hat to fall off and break the control panel causing it to malfunction and explode, throwing Hater near Wander. Wander holds out his arms to catch Hater, but they both are thrown into the pit. Sylvia is left behind along with Peepers and the Watchdogs, who gang up on her.
Later in the prison dimension, Hater contacts Peepers, but is crowded by a gang of thugs, who punch the living daylights out of him. Wander comes upon the fight and stops them; the thugs immediately recognize Wander, who helped them out in the past. The thugs were all thrown into the pit by Hater. The thugs once again gang up on Hater, but Wander stops them, saying he does not want "[his] friends hurting [his] other friends", shocking Thrax. Wander makes it clear that he sees Hater as a friend. Hater attempts to deny this, but just as the thugs attempt to attack him again, Hater decides to go along with this friendship, by pretending to be buddies with Wander. They prove their "friendship" by showing the others their secret friendship handshake. Thrax, the leader of the thugs, warns Hater that he better not be joshing them.
Later that night, Hater is by himself making plans to obliterate Wander when he smells a feast being eaten by the others. The hungry Hater decides to steal a morsel of food but is thwarted by Thrax. Wander comes to him and reveals he couldn't get any food since the thugs ate the last of it, so offers a plate of indigestible items such as an eyeball, a centipede, and what appears to be feces. Hater attempts to throw the food to the ground but is once again caught by the thugs. He eats it but throws up.
Afterward, he sees Wander under a shelter he made from sticks. Wander offers Hater a seat next to him, but Hater refuses, only to once again be caught by the thugs. A single snowflake falls, followed by a blizzard, which covers everything but Wander, who rubs his hands together to warm them up. Wander decides to warm Hater with a hug, but Hater leaves the shelter. But the thugs change his mind. Wander hugs him again, and they soon fall asleep.
Hater wakes up the next morning to find Wander singing about how they are now Best Friends Forever. Hater is confused by this song but soon finds himself enjoying being buddies with Wander, and even ends up singing a verse happily. This later turns out to be a nightmare Hater was having. When Hater notices Wander starting to play the same song, he tosses him to the ground and sees the thugs seemingly coming after him, and attempts to impress them by singing the song to Wander.
It turns out the thugs were actually running from a Sand Snapper. Wander gets trapped in the whirlpool and screams to Hater for help, but Hater simply smiles and dances. The thugs arrive to make a chain with Hater on the end to get Wander out of the vortex. Hater pretends to attempt to catch him but claims that Wander is too far, prompting Thrax to tell Hater that Wander is being consumed by a Sand Snapper, which is extremely painful, which intrigues Hater. Hater unwillingly tells Wander to grab his hand, but Wander expects the sentence to end with something else, so Hater says, "...buddy". After hearing that word, Wander grabs Hater's hand and is rescued from the vortex. Wander admits he does not like the place but is relieved that there seems to be good in Hater after all.
Suddenly, a beam of blue light comes out from the sky. Hater assumes Peepers is rescuing him and shows his true attitude towards Wander by throwing his half of the "Best Buds" pendant to the ground. It turns out that Sylvia is the one bringing the beam down, and she brings Wander up. The thugs attack Hater once again. When he gets back on Hater's ship, Wander decides to rescue Hater as well as the rest of his thugs, since he still considers them buddies. Wander is about to say "Later Hater", but stops himself and calls him "Buddy" and gives Hater his half of the "Best Buds" pendant. This upsets Peepers, who always assumed Hater was his best bud and leaves in tears, leaving the thugs to attack Hater once more.
Commander Peepers, discouraged that Hater is "best buddies" with Wander instead of him, cries himself to sleep in his bedroom. He begins to angrily trash, and then sadly fix, everything that reminds him of Hater in his room.
- Jack McBrayer as Wander
- Keith Ferguson as Lord Hater, Inmate 2 (uncredited)
- Fred Tatasciore as Thrax
- April Winchell as Sylvia
- Tom Kenny as Peepers, Inmate 4 (uncredited)
- When Wander gets caught by Lord Hater he is holding his hands, but when they are shown falling into the portal he is holding him by the waist.
- During the song, while Wander and Lord Hater are wearing flower necklaces and wreathes, Wander's necklace doesn't turn with his body when he turns to the side.
- When Wander sings the line "We'll still be best buds anyway" his upper hair strand cuts off into the edge of his hat.
- Wander and Hater fall through the portal together, but when they come out they are falling separately.
- Peepers wears half of the "Best Buds" pendant and gets upset to Lord Hater over it even though Hater said they're not friends in "The Prisoner".
- Lauren Faust said the song "Best Friends Forever" took her inspiration from the songs "Jolly Holiday" from Mary Poppins.