Green Ghoul is a one-time character in The Thundermans. He appeared in the first Halloween special, Haunted Thundermans. He is a ghost that was once imprisoned by Hank Thunderman but escaped after Miles and Louie accidentally freed him.
He took control of Phoebe and almost killed Hank, but was foiled by Max. He battled the Thundermans and Hathaways and was defeated when Phoebe and Max combined their ice breaths and Hank threw him into the Ghost Cage.
Green Ghoul once attempted to take over the world. He almost succeeded but was stopped by Hank. When in ghost jail, he was freed when Louie made a crack in the wall. In order to get revenge on Hank, Green Ghoul possesses Chad to get close to Phoebe. Eventually, Max realized that he was the Green Ghoul with his ghost-tracking device, but Phoebe didn't believe him. After he possesses Phobe, Max tried to fight him off, but he fled and went straight to the Hathaways house to deal with Hank. Noticing that the adults were accidentally imprisoned, the Green Ghoul only frees Hank in order to deal with him personally. As Max and Taylor entered the room, Max was offered the chance by the Green Ghoul on becoming a real supervillain by joining him. As it first appeared that Max was willing to accept the offer, he attempts to ice breath him a few times. After being kicked out of Phoebe's body by Miles, Max and Phoebe both combine their ice breath on him and successfully froze and imprisoned the Green Ghoul. Hank then used his super strength to throw the Ghoul into the Ghost Cage and he was then sent back to ghost jail.
- Ghost Physiology: As a spirit/ghost, The Green Ghoul has all the standard/same ghost powers as Louie, Miles, and Ray Preston, which are Invisibility, Intangibility, Flight/Levitation, Teleportation, Overshadowing/Possession (the power to possess people and objects), Shapeshifting, and Telekinesis. He can use his ghost powers by snapping his fingers. If he possesses a superhero, he would then combine his ghost powers with their superpowers and become unstoppable.
- Voice Mimicry: The Green Ghoul used his overshadowing throughout the crossover, which he often switches between his voice and the person he is overshadowing, this ability is marked by an effect, such as glowing eyes when in a human host.
- He is a parody of the Marvel villain, Green Goblin.
- The Green Ghoul is a level 13 ghost surpassing Ray Preston and the only highest level ghost so far.