Chip Skylark has only had a handful of major appearances. However, him being voiced by Chris Kirkpatrick, along with being one of the few genuinely nice characters in the show has greatly endeared him to fans.
Norm the Genie, was a three-appearance villain who became a Draco in Leather Pants among the fandom.
Ms. Doombringer, a highly competent fairy hunter who appeared in just one episode but has people asking for more.
Molly and Dwight have only shown up in one episode (Wishing Well), but their personalities and dynamic with Timmy has quickly endeared the duo to fans and many wished they appeared beyond their sole episode. Molly in particular became incredibly popular due to her gothic personality and it didn't take long for shipping between her and Timmy to ensue as a third option for those who don't want Timmy with Trixie or Tootie.
Remy Buxaplenty to some degree - he appeared in one episode to challenge and lose to Timmy in a duel, and disappeared after that. All the same he had a fairly significant following and a tendency to be shipped with Trixie Tang - who didn't even interact with him in "Remy Rides Again" when they appeared in the same episode - and years later was brought back for a small handful of new episodes.
The Gilded Arches because even though he first appeared in the webtoons, he became popular enough to appear in "Breaking Da Rules".
Dark Laser. Initially, he was a one-off villain. Then he made an appearance in the fifth season as a continuity nod, but by the sixth season, he'd become a semi-regular, even having a major part in the season finale.
Anti-Cosmo is quite popular among the fandom, especially the idea of Timmy being his godchild. No wonder why Foop is seen as a Replacement Scrappy for many fans.
Maryann, despite being a one shot character, is one of the show's most memorable villains due to causing World War 1 and, indirectly, every war after that.
Timmy's Gender Bender alter-ego, Timantha. Despite only appearing in "The Boy Who Would Be Queen", she eventually became popular enough to appear in Breaking Da Rules as one of Timmy's alternate forms.
Gary, Timmy's imaginary friend, who only ever appeared in two episodes (one of which was just a continuity nod) but is also very popular with the fandom.
Princess Mandie, one of the few competent villains in the series who looks like she came out of Danny Phantom instead. She only appeared in three episodes (plus a cameo in a fourth).
Principal Waxelplax, for being a Big Beautiful Woman, her relationship with Crocker, and being one of the nicer characters on the show.
