Foop breaks the fourth wall twice: When he says the only thing Poof can say is his name and when he says he can't understand what Poof says, unlike the whole school.
It's revealed that Foop has heat vision just like Timmy.
The music in gym class is the same as the one in Odd Ball.
Timmy, Cosmo, & Wanda are only in the beginning and end of the episode, marking this one of the few episode where Timmy, Cosmo and Wanda aren't the main characters, along with "The Big Scoop", the Crash Nebula special, and "Love Triangle".
Poof is the main character in this episode.
Apparently the phrase "saved by the bell" is used in a literal sense in Spellementary School since as explained by the teacher, Foop's plan for revenge was ultimately foiled by the final bell.
When Foop says that 2 + 2 equals Death, he is technically correct, as in Chinese, Japanese, and Korean, the words for "four" and "death" are similar.
The Three Rs - When Foop first arrives in front of the school, he says "It's time to teach Poof the three Rs: Reading, 'Riting and Revenge!". This is a play on the saying "Reading, Writing and Arithmetic".
Also, it makes a reference to the saying "Reduce, Re-use and Recycle.
There is no mention of the events that transpired in Playdate of Doom nor any reference to how Foop got out of the parallel dimension.
When the school is about to be sucked into the black hole, Foop's in his regular clothes.
Even though Cosmo was the second-to-last fairy baby to be born, the school is still full of fairy children.
Other students may be elves, since they are not of a certain shape like Poof or Foop.
After Poof saves Foop from detention, Foop says he was yet AGAIN saved by his nemesis. But Poof has never saved him before, unless he helped Foop escape the other dimenson. However, that is most likely impossible as this would be something Poof would never do due to Foop wishing to take revenge on Poof.
Foop swallowing a sprite while laughing evilly.
Foop talking to himself.
The students throwing food at Foop.
Almost everyone says, "Foop, spelled backwards!" when they mention Poof. This causes Foop to get angry because he thinks that it was him, not Poof.