The Green Ghoul is the main villain in the Thundermans and Haunted Hathaways crossover Halloween special "The Haunted Thundermans". He is a ghost that was once imprisioned by Hank Thunderman, but escaped after Miles and Louie accidently freed him.
In order to get revenge on Hank, Green Ghoul possesses Chad to get close to Phobe. Eventually, Max realized that he was the green ghoul with his ghost-tracking device, but Phobe 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 accidently imprisioned, 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 Phobe's body by Miles, Max and Phobe both did their ice breath on him and successfully froze and imprisioned the green ghoul.