The Zombie Horde appear, and are the main antagonists of the Gravity Falls episode "Scary-oke".
Dipper accidentally summons a Zombie Horde while trying to prove his point about the secrets of Gravity Falls to a couple of Government Agents. As the creatures advance, they scare off the party-goers, and Mabel scolds her brother for doing the one thing she told him not to. Soos attempts to protect them, though he gets bitten almost immediately and transforms into a zombie himself.
As Dipper, Mabel and Waddles flee, Stan is in his lab contemplating Dipper’s stubbornness, unaware of the situation that is going on, he resumes his work, citing that he has too much to do to worry about the kids. However, he quickly changes his mind and turns to his monitors, realising the danger they are in he rushes to save them just as they are about to be eaten. He sends the kids to the attic as he fights off the advancing monsters and reveals that he has always known about the paranormal activity in Gravity Falls, and that he was denying it to keep Dipper and Mabel out of danger.
Just as Dipper is about to give up hope, stating that Journal #3 did not contain any answers like it normally does, Mabel noticed that new text is visible when the page are shone under black light. Dipper discovers that zombies can be defeated by shattering their skulls with a three-part harmony, and Mabel points out that a karaoke number is the perfect solution. From the roof, Mabel introduces the three as “Love Patrol Alpha,” and Dipper and Stan less than happily begin singing “Taking Over Midnight” with her. The song works, the zombies are destroyed and the Pines cheer.