|~ The Pistachions helping their king taking a selfie.|
The Pistachions are the major antagonists of the first season of the Disney XD series Milo Murphy's Law. They are giant anthropomorphic pistachio monsters (led by King Pistachion, and later by Derek) bent on taking over the world at all costs.
Although the Pistachions didn't appear much in the first season, their origins were shown in the episode "The Substitute", where Milo Murphy and his friends accidentally created a sentient blob that attacked the students and two time-travelling agents named Vinnie Dakota and Balthazar Cavendish. In the end, the blob left the school and came into contact with a broken pistachio sapling on the lawn, causing it to be replenished to its former glory.
In the hour-long special "Missing Milo", Vinnie and Balthazar were contacted by their boss Mr. Block of their mission to ensure that the pistachios' existence remain intact by the year 2175. Locating the growing pistachio sapling at the school lawn, the two agents decided to preserve it to accomplish their mission. However, while they contact Mr. Block about their success, they spot through their communicator that Mr. Block is being attacked. Thinking of it as a joke, Vinnie and Dakota decide to travel back to the year 2105 by loaning a time-travelling limousine from their fellow agents Brick and Savannah, accidentally taking Milo along with them.
Arriving back to their time, Milo and the agents are horrified to learn that a horde of giant pistachio-like monsters (known as the Pistachions) have taken over the world and captured much of the human population (including Mr. Block) in giant pots. Upon spotting the trio while taking a picture of his own family with his phone, King Pistachion orders his horde to capture them. Realizing now that this isn't a prank of any sorts, Vinnie, Balthazar and Milo soon learn that the pistachio sapling is actually King Pistachion in his early days, as he would grow on to become a more powerful monster and create his own horde to take over the world; even admitting that he had one of his sons to eat up a Congressman during the takeover.
Realizing their mistake, Milo and the agents went back in their limo to destroy the sapling, but having already realized their intentions, King Pistachion has his own time-travelling vehicle to beat them to it. Arriving to the school, the Pistachions confront Milo's friends and sister as they were investigating Milo's disappearance. King Pistachion orders his horde to kill the kids, but Milo and the agents arrive to stop them in time. Using a formulated plan utilizing Murphy's law, Milo gets his friends and the agents to fight back against the pistachios while he grabs hold of the pistachio sapling, hoping to destroy it. However, King Pistachion grabs Milo's friends and the agents, threatening to kill them all if Milo doesn't step away from the sapling. Using a woodpecker flute, Milo manages to call up several woodpeckers to attack King Pistachion to save his friends and the agents, but King Pistachion manages to grab him, hoping to finish him off. Anticipating the possibility of being captured, Milo orders his dog Diogee to pee on the sapling, knowing that several types of pistachios are very vulnerable to urine.
With the sapling destroyed by the dog urine, the Pistachions get erased from existence for good, but not before their dying king vows revenge on Milo for ruining his plans. However, one Pistachion survives by stumbling through the time stream, ending up on the year 1955. Smiling at this, the Pistachion happily runs off as he intends to get revenge on the heroes for wiping out his race from existence. It is unknown what happened to the Pistachion afterwards.
Fungus Among Us
In the episode "Fungus Among Us", it is revealed that the Pistachion who escaped through the time stream was none other than King Pistachion's son Derek, who is bent getting revenge on the heroes for wiping out his race and defeating his father. Disguising himself as an intern for the Dr. Zone show in 1965, Derek managed to formulate a certain plot that involves extinguishing the human race and replacing them with new Pistachions in disguise. This causes the time stream to change, nearly wiping all of the human race with new Pistachions.
With only Milo, Diogee, Dakota, Cavendish & Orton Mahlson remaining as the only ones to evade the Pistachions' capture, they seek to find the world's first time-traveler Professor Time to get some answers. However, in the episode's cliffhanger ending, the five end up meeting the evil scientist Heinz Doofenshmirtz (who too has avoided being imprisoned by the Pistachions for unknown reasons) after being trapped in his lair by accident.
The Phineas and Ferb Effect
It is later revealed that Derek himself spent the next 50 years expanding his race, which allowed enough Pistachions to take over the world. They are seen rounding up most of the characters (including the main characters' families and friends) and turning them into monstrous Pistachions with Derek's newly developed 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).
Fortunately for the heroes, Doof was able to create a new time machine to gather up orange soda from 1965 that can easily destroy Pistachions just as his future self (revealed to be the actual Professor Time) arrives to bring Orton back to 1955, where they used the orange soda to destroy the 1955 Derek. With his past self destroyed, the future Derek and the other Pistachions fade away from existence, which restores up the original timeline for good, turning everyone back to normal.
As of currently, the Pistachions are completely erased from existence.