* ActorAllusion: In the two-part episode, "Brown Evil", Billy mistakes Hoss Delgado for a wussy video game character named Pat the Baker, both of which are voiced by Deiderich Bader. Similarly, in the actual video game of the series, when Hoss wins, he says "[[NapoleonDynamite Bow to your sensei!]]"
** Dean Toadblatt is voiced by the late John Vernon, who is remembered by many as the antagonistic Dean Wormer from ''Film/AnimalHouse''.
** In the [[ChristmasSpecial Christmas Special]], the vampire Baron von Ghoulish, voiced by Creator/MalcolmMcDowell, is first seen filing his teeth and [[Film/AClockworkOrange singing Singin' In The Rain]].
** Two episodes feature Creator/KurtwoodSmith as Grim's dad, who is pretty much a skeletal [[That70sShow Red Forman]] in terms of appearance and mannerisms.
* CrossDressingVoices: Irwin is voiced by Creator/VanessaMarshall, Pud'n is voiced by Jane Carr, and Nergal Jr. is voiced by Debi Derryberry.
* FakeBrit: Eris. What makes it funny, however, is that she's supposed to be a GREEK goddess. Furthermore, she also speaks like a ValleyGirl.
* HeyItsThatVoice:
** Creator/RichardStevenHorvitz as Billy [[TalkingToHimself and]] Harold
** Creator/DavidWarner was the first voice of Nergal (Martin Jarvis [[TheOtherDarrin replaced him]])
** Music/GreyDelisle as Mandy
** Greg Eagles as Grim, using his [[WesternAnimation/CrashBox Captain Bob]] voice. He [[TalkingToHimself also voices]] Sperg the bully.
** Creator/DiedrichBader as Hoss Delgado and Pat the Baker (a wussy video game character that Billy likes). Lampshaded in "Brown Evil", when Mandy and Grim say, "it's Hoss Delgado!" while Billy yells, "It's Pat the Baker!".
** Don't forget Music/WeirdAlYankovic as the Squid Hat (and the announcer for the video game adaptation)!
** Dean Toadblatt's voice actor is John Vernon, the same guy who played [[Film/AnimalHouse Dean Wormer]], [[ActorAllusion which explains why he yelled "Gunderstank House!" after getting pranked]] on the episode where Billy and Mandy go to a Hogwarts-style school for kid wizards.
** General Skarr is Armin Shimerman, aka [[Series/StarTrekDeepSpaceNine Quark]] and [[Series/BuffyTheVampireSlayer Principal Snyder]].
** Nergal Jr. is [[WesternAnimation/TheAdventuresOfJimmyNeutronBoyGenius Jimmy Neutron]].
** Creator/JenniferHale is Billy's mom.
** Creator/RachaelMacFarlane (Hayley Smith on ''WesternAnimation/AmericanDad'' and Creator/SethMacFarlane's sister in RealLife) is Mindy and Eris.
** And who could forget [[http://www.youtube.com/watch?v=wWeP3u5hY8w Good Ole' Voltaire]]
** Jack O'Lantern is [[WesternAnimation/BuzzLightyearOfStarCommand Zurg]]. (In the video game, [[Creator/MauriceLaMarche he's]] [[WesternAnimaiton/CodenameKidsNextDoor Father]].)
** Creator/BettyWhite is Mrs. Doolin in "Who Killed Who?"
** Creator/ChristopherLloyd is the Catastrophe Snail in "Dumb Luck".
** [[LizzieMcGuire Matt McGuire]], moonlighting at Cartoon Network as [[Film/HarryPotter Nigel]] [[{{Expy}} Planter]].
** Creator/PatFraley ([[WesternAnimation/TeenageMutantNinjaTurtles1987 Krang, Baxter Stockman and Casey Jones]]) was Dr.Fear/Clortho.
** Grim's Mom is [[WesternAnimation/CodenameKidsNextDoor Numbuh Two's Grandmother]].
** The Latin dub has a sort of CastingGag with [[Film/HarryPotter Nigel Platter]], as the VA that voiced him actually voiced Harry too.
*** The same goes for Boo Boo and Fred Flintstone when they had their cameos. They had their original [=VAs=] too.
** In 'Here Thar be Dwarves' Creator/MichaelDorn ([[Series/StarTrekTheNextGeneration Worf]] and IM Weasel) shows up as King Beardbottom, and RLeeErmey shows up to try and block out the battle "for their younger viewers".
* KeepCirculatingTheTapes: The first season was released on DVD but that has long since gone out of print, the same can be said for Big Boogey Adventure's DVD, several episodes were released either on Cartoon Network Holiday Compilations or as extras on other [=DVDs=], thankfully the entire series (Sans Big Boogey Adventure, the Christmas special and Underfist) is available on iTunes and the first 39 episodes listed as seasons 1 and 2 are on Netflix.
* OneOfUs: Fictional example. In the "Brown Evil" episode, whereas Billy prefers playing a cheesy cooking game named "Pat the Baker", Mandy prefers a much more violent ''Franchise/ResidentEvil'' parody featuring Hoss Delgado. At the end of the episode, Hoss states that he never leaves home without the former example and is seen cheerfully playing it alongside Billy.
** One episode, directly after the title song, has Mandy say, [[{{Film/Freaks}} "We accept you. We accept you. One of us."]]
* TheOtherDarrin: In the first Secret Snake Club episode, the short leader is voiced by Creator/TomKenny, while he is voiced by Creator/BillyWest in the second.
* TalkingToHimself: There are a few examples in the series, the most notable being Billy and his father Harold (both voiced by Creator/RichardStevenHorvitz), and the few scenes that Grim and Sperg have together throughout the series (both of them are voiced by Greg Eagles).
* WhatCouldHaveBeen: The ''Underfist'' movie was meant as a possible pilot for a new spin-off series (made a bit more obvious due to the new animation style), but Cartoon Network turned it down. Some sources say that the creator, Maxwell Atoms, pitched the idea as a prank.
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