Mr. Pickels is the first major non-animal character in the show, though he is the second non-animal character in the show, the first being The Cursed Idol.
Mr. Pickels is also the first, and so far the only, fruit character in the whole series. (Although he is often mistaken as a vegetable, scientifically, he is considered a fruit.)
Some presume that Mr. Pickels is just a figment of Lammy's imagination and that Lammy is killing everyone herself. However, if Mr. Pickels isn't a living creature, it is unknown how an "ordinary pickle" can suddenly move to different spots.
Mr. Pickels and Lammy are the 21st and 22nd (or in other words, the last two) characters to come back to life after dying, as they both died in All In Vein and came back in You're Kraken Me Up.
He is the only character to match the exact color of his "species".
He is the smallest Happy Tree Friend.
In Royal Flush, he killed Flaky single-handedly by impaling her on a plunger and flushing her corpse down the toilet without the presence of Lammy. This further indicates the possibility that he is a living creature after all, although it is possible that this was just a random accident.
He and Lammy are the only main characters who have not appeared in the TV series.
Mr. Pickels may be based off Mr. Potato Head from the movie Toy Story.
Mr. Pickels may be a reference to Mr. Hankey the Christmas Poo from South Park, who is also an (ostensibly) imaginary character; his shape is even very similar. He may also be a nod to Mr. Hat, an inanimate puppet who has been seen to be able to move even when not being controlled by Mr. Garrison.
Lammy and Mr. Pickels' actions may be a reference to "Kid vs. Kat", as Lammy is always being blamed for what Mr. Pickels does, similarly to how Coop is blamed for Kat's actions.
In the episode All In Vein, Mr. Pickels' dead body was laying next to a dead animals bin. This might be evidence that further proves that Mr. Pickels is indeed a living creature.
Mr. Pickels dies in 1 out of the 7 episodes he appears in. (2 if one counts Breaking Wind)
Lammy is the only female that hasn't been killed by Mr. Pickels, for obvious reasons. In contrast, the only male character that he has killed is Handy.
Mr. Pickels is one of the three characters to never kill every character in one episode, the other characters are Lammy and Cuddles.
Lumpy is the first and so far only character to kill Mr. Pickels, in All In Vein.
He has only one death in All In Vein, the least out of any other character (and even this is debatable). This is obviously because of his late arrival.
He is the only main character whose deaths are all debatable, thus making him the only character to not die.
He has the highest survival rate out of all the main characters in the series.
Despite his villainous role and being known for killing other characters, he is the only main character who has never been responsible for all the deaths in an episode.
He is the only main character who has never killed a character without the help of another character (while he technically killed Flaky single-handedly in Royal Flush if it weren't for Lammy handing the sandwich he was in over to the girls Flaky wouldn't have been killed by him).
He and Splendid are the only the only main characters who've never featured in an episode.
Mr. Pickels is one of the few characters who have never had a real occupation. The others are Lammy and Cub.
Mr. Pickels is one of seven characters not to have the same kind of eyes as the other characters. The other six characters are Lumpy, Nutty, Cub, Lifty & Shifty (from the TV series onwards), and The Mole.
Mr. Pickels is one of the few characters who have never been the last character to die in one of their starring roles. The others are Cro-Marmot, Lammy, and Mime.