The Pumpkinator would return in "Escape from Unwish Island".
Trixie and Veronica are not seen morphing into their costumes.
The popular kids are probably the controllers of the Jack-O-Bots.
The Jack-O-Bots are an allusion to the "Autobots" from the Hasbro toy line,Transformers, except that the Jack-O-Bots are evil, while the Autobots are good. (The Jack-O-Bots being evil makes them similar to the Autobots' enemies: the Decepticons)
Vicky: "Where did you get the costume? Dorks R Us?" - Dorks R Us is an allusion of the store Toys Я Us.
The Jack-O-Bot names are not only named after minerals/metals, but are also similar to names of Pokémon video games, including Pokémon Gold and Pokémon Silver (for the Game Boy Color), Pokémon Ruby (for the Game Boy Advance) and Pokémon Diamond (for the Nintendo DS).
"The Twilight Zone": In the episode "The Masks", four benefactors are turned into monsters by the hideous masks each wears.
When Veronica, Trixie, and the other rich kids appear on Timmy's doorstep, Veronica's pupils are pink. After Trixie tells her to polish her costume, Veronica's pupils return to their normal color (blue).
When Cosmo and Wanda appear as cats during the scene where Timmy meets with Mark Chang, Wanda is green and Cosmo is pink.
Although the Jack-O-Bot costumes are wished back into normal inanimate objects, they appear later on Unwish Island as sentient beings.