|“||Nobody talks to the boss about this.||„|
|~ Dennis about the heroes escaping after eating several Pistachion sprouts.|
He was voiced by Jim Ward.
Fungus Among Us
Dennis, along with his fellow Pistachions, were created by Derek following the latter's travel to the year 1955. Determined to avenge his deceased father King Pistachion, Derek formulated a plot of changing the timeline, allowing the Pistachions to take over the world in the present, rounding up all humans.
Dennis was first seen spotting Milo Murphy, Orton Mahlson, Balthazar Cavendish, Vinnie Dakota and Diogee, so he orders several of his Pistachions to catch them. The heroes forced to lock themselves up in a disposal room. Dennis sends in several Pistachio sprouts to break inside the room and kill the heroes, but Dakota just grabs the sprouts and eats them up, much to Dennis' anger. This provoked an angry Dennis to break down the door, but the heroes made it to the sewers, where they used a boat to escape. Upon witnessing the heroes escape, Dennis tells his fellow Pistachions not to disclose the incident to Derek, but one of them informs that Derek has made a call and wants to talk to Dennis, much to the latter's frustration.
The Phineas and Ferb Effect
Dennis was seen as he managed to capture Milo and his friends (as well as Phineas and Ferb). He also informed them that he and his fellow Pistachions don't replace people with plant replicas anymore, and that they actually intend to turn them all into new Pistachions with the use of Derek's new machine called M.U.L.C.H.T.P. (Machine Used for Literally Converting Humans To Plants, though the last two letters are silent as Derek claimed) to take over the entire world, even using it to turn all of the main characters' families and friends into Pistachions.
Fortunately for the heroes, the former evil scientist named Heinz Doofenshmirtz managed to build a time machine to sent Orton back to 1955, where they destroyed Derek with orange soda. This event is what erased Derek and the Pistachions from existence, and it can be implied that Dennis himself is erased from existence as well.