- Actor Allusion: In one scene of "Murphy Murph and the Feng Shei Bunch", Marco wears a Chips helmet.
- Channel Hop: It aired its first three episodes on Cartoon Network at early morning graveyard slots in late 2000. When [adult swim] first debuted in 2001, it moved there as it fit their demographics (it somewhat fits as Adult Swim has been considered a separate network for ratings purposes since 2005).
- DVD Commentary: Present in all four seasons, although they did little to elaborate on production, but were there for additional jokes. Season 3 had a particularly memorable one called the "Commentary of Hatred" where blogger Karl Olson rips the episode "Tornado Shanks" (widely believed to be the beginning of the show's Seasonal Rot) apart.
- Executive Meddling:
Sparks: Your "lord"? It's a baby with a freaking gun, roasting over a flood light!
- "Bebop Cola" was originally called "Jazz Cola", until the legal team found out an actual cola company had the rights to the name, and altered it to avoid legal issues.
- The episode "Feast of Alvis" was supposed to be a straight-up Christmas Episode... until the executives rejected it. Jesus was then replaced with Alvis, the worship of whom served to make Murphy look that much crazier.
- Marth Debuted in "Smash Bros.": The original series (Sealab 2020) never aired outside the U.S., so all dubs of Sealab 2021 suffer from this.
- Promoted Fanboy: mcheshpants420, a member of the [adult swim] message board, who wound up writing "Fusebox" and "Dearly Beloved Seed". It's generally theorized that this is mc chris, one of the writers on the show and the voice of Hesh, simply mocking the fans.
- Throw It In!: Aside from the Hilarious Outtakes that sometimes play over the end credits, several lines throughout the series appear to be lines from the recording studio where the actor was talking to the director or otherwise cracking up. Debbie Love seems to get quite a few of these, and one particularly odd one involves Stormy, sounding unusually eloquent, arguing about whether the line should be "sticking a staple in their eye" rather than "sticking a stapler in their eye", finishing with "maybe I'm being too literal, I mean, this is a cartoon."
Trivia / Sealab 2021