Attack of the Graveyard Ghouls

Attack of the Graveyard Ghouls was the eleventh book in the Goosebumps Series 2000 book series. It was preceded by Headless Halloween and followed by Brain Juice.

Plot
Spencer Kassimir and his friend, Audra Rusinas, visit a graveyard, where two young boys, Oswald and Martin Manse, are buried together under one tombstone. After Spencer knocks over the headstone, the zombie-like, ghoulish figure of Oswald was back from the dead, ends up pushing Spencer out of his body and possesses it, leaving Spencer in the spirit world with other souls who tell Spencer about how evil Oswald and Martin were when they were living. Spencer tries to get back home and confront Oswald by possessing several bodies.

After failing to convince him, he seeks Audra's help. But there, it is revealed that Audra's body was already possessed by Martin when they first visited the grave. After finding Audra, she and Spencer try to stop the two ghoulish brothers. After doing a special ghoul dance, Martin and Oswald (who are ghouls) die, Audra and Spencer get their bodies back. Though in a twist ending, Audra and Spencer end up with each others' bodies.

Trivia

 * This book wasn't made into a television series along with The Haunted School, Ghost Camp, Egg Monsters from Mars, I Live in Your Basement! and Monster Blood IV.
 * The Graveyard Ghouls will appear in the 2015 Goosebumps movie.