Foop's first sentence is "Hello Clarice, I mean mother." This is a reference to The Silence of the Lambs where Hannibal Lecter greets the main character, FBI Agent Clarice, this way. His father, Anti-Cosmo, frequently says "Hello, Clarice" as well.
In his first few appearances, Foop seems to suffer from a form of identity disorder, in which he would often enter brief conversations (mostly arguments) with himself over his actions. This trait was dropped in later seasons, however.
Foop calls Cosmo, "Uncle", and Wanda, "Auntie", despite that they are actually the counterparts of his parents rather than siblings.
The alternate dimension that Foop winds up trapped in is a parody of the phantom zone from Superman II.
Foop's alternate title as "Anti-Poof" is probably a reference to the fact that Anti-Fairies are named after their corresponding fairy, but with "Anti-" placed before their name (Anti-Cosmo, Anti-Wanda, Anti-Jorgen, etc.). Foop seems to be the only exception so far, as his name is his corresponding fairy's name spelled backwards.
Ironically, in Anti-Poof, it is revealed that Foop hates his own name.
He is the only Anti-Fairy that has not experienced a Friday the 13th on the show yet.
In "Timmy's Secret Wish", Foop doesn't even consider the possibility that if he manages to undo the existence of Poof, he would be undone until Jorgen Von Strangle points this out. This may indicate that he is not as intelligent as his father, Anti-Cosmo.
Foop appeared three times as a villain in Season 8, more than Vicky's and Mr. Crocker's appearances as villains.
In Spellementary School, Foop tries to be the most popular student at the school and fails to do so. This is a big switch, considering in his debut appearance, he states clearly that as Poof's opposite, he must be feared and despised throughout the universe.
Even though he is the son of Anti-Cosmo and Anti-Wanda, he has appeared alongside them only once.
In The "Terrible Twosome", Foop has the Terrific Twos in the second half of the episode, while Poof has the Terrible Twos.
In "Scary GodCouple", Foop was made Vicky's Anti-Odd Parent, despite that in Balance of Flour, it was mentioned that no Anti-Fairy can be the Anti-Fairies of a child.
Foop experienced a Fairy-clipse in "When L.O.S.E.R.S. Attack".
As mentioned by Foop in Timmy's Secret Wish, his tears are made out of acid.
Foop was supposed to be the antagonist of Poof, until "Timmy's Secret Wish" and "When L.O.S.E.R.S. Attack", where he turns into the antagonist of Timmy. However, it's stated in both of those episodes that he wants to go after Timmy because he gets in the way of him going after Poof.
It appears that by the end of "School of Crock", Foop might have abandoned his antagonism towards Poof as he is shown being thankful to Poof for saving his life and apologizes for trying to annihilate him all the time. This also may be the reason why Foop attends to Cosmo and Wanda's work anniversary in the following episode "The Past and the Furious" and his new focus on antagonizing Timmy Turner.
He is the one responsible for the naming of "L.O.S.E.R.S." after his colleagues failed to present a proper name.
He's one of the few anti-fairies whose voice isn't provided by the same actor who plays the main fairies counterparts.
Despite being connected to Poof, he appeared in seven episodes where his counterpart did not appear.
Even though he is an enemy of Timmy Turner, there have been some episodes (particularly in later episodes) where he was neutral or even friendly to him.
This caused him to become more of an on-and-off antagonist, rather than a pure-evil villain like he originally were.
Allusions
Stewie Griffin - He is similar to Stewie Griffin from Familly Guy in how they act and speak and in their initial hatred towards their mothers. Like Stewie, he eventually got over it.
They both speak in British accents as well and are fictional villainous infants who are capable of speech and sound like fully grown men.
Running Gags
Adding "of doom" sometimes at the end of sentences.
Quotes
"And now my goody two shoed nemesis of which I don't know of yet, I shall finally DESTROY YOU!!! I've waited my whole life for this moment! All 6 hours and 45 minutes of it! What?!?"
"Round one to you, round one."
"There's a new sheriff in town and his name, unfortunately, is Foop!"
"Time for a Playdate...of DOOM!"
"If you're always worried about crushing the ants under your feet you will never walk."
"Hello Auntie Wanda and Uncle Idiot, I mean...Cosmo."
Foop: "Knock knock!"
Annoyed Little Elf: "Ugh, who's there?"
Foop: "DEATH!!!!!"
[Foop is the only one laughing]
Mrs. Powers: "Now Poof, it's your turn to give your speech."
Foop: "WHAT!? He only said his name! That's all he EVER says!"
Foop: "Poof, if you join me, I'll name you vice-president."
Foop: [to self] "I thought I was going to be vice-president!"
Foop: "Quiet! you're the minister of agriculture."
Mrs. Powers: "We have a new student in our class, and his name is Foop!
Foop: "Oh, you're too kind."
Mrs. Powers: "...spelled backwards!"
"Past morons and future victims, slaves, underlings, and minions: DEATH!! PAINFUL FIERY DEATH! You wonder "Am I a leader?" DEATH!!!!!!! And so, in conclusion, vote for me or death, painful fiery death. Thank you very much."
"It's Foop, you triangular twit! One F, two Os, one P! It's not that difficult!!"
(After he had been born) "Hello Clarice, I mean mother."
"Think of it: Poof and Foop, together we make...POOP!"
"OH COME ON! WE ARE IN THE REAL WORLD!! GET SOME HELP!!!"
Poof: "No problem, Foop! Do you think we can be friends now?"
Foop: "Oh, absolutely not, no."
"Weird! Poof can talk now! It's strange, but I'm gonna miss the way he used to say "Poof, poof". (gets hit by a hammer he installed)
"Anyway, now, it's beddy-bye time for Wesley! I shall read him my favorite children's book! If you feed a mouse a poison cookie, it dies!' The end, sweet dreams.
"Here comes hot lava! Hot, scary, deadly. Just like me!"
