During production of the first season, only Kristen Bell and Ted Danson knew about the twist from the beginning. Kristen recorded a video of the remaining cast members being told about the season 1 reveal. Their reactions are face-holding shock from Jameela, surprised giggling and hiding behind clothing from D'arcy, a giant "Oooooooh!" from Will, and Manny just... flailing and twitching as he tries to process everything.
Doubly funny when, in the accompanying podcast, D'arcy, Jameela and Will all admit to being worried that the meeting was to tell them all they were being fired...whereas Manny thought they might be being 'promoted' (given more prominent roles due to Danson & Bell leaving the show).
Season 1's gag reel is hosted in-character by Trevor with series appropriate meta-ness (negative points for hosting a party about making a TV show, for instance) as well as the gags and bloopers themselves. Standout moments include:
The different improvisations Jacinto and Carden did; specifically, when Jason tells Michael what his vanity plate says, how he died ("stingray jousting accident" and "escaped zoo animal rampaging through a mini-golf course" are both present), and when Janet misidentifies a basketball (one standout: "Look, Michael, a witch... Burn her.").
The official Youtube channel livestreamed and uploaded a five-hour video of what Janet does in her void. A good 90% of that video comprises Janet just happily standing there in silence (with the occasional change in arm position and camera cut), waiting for someone to ask for her assistance. Whenever she is needed, she bings out until she's done. Which leads to the other 10% of the video—an empty, unoccupied white void.
Visual effects producer David Niednagel had Joe Mande (the guy who plays Todd the lava monster) wear a ridiculous greenscreen suit for the role, knowing full well that it was completely unnecessary.
The season 3 gag reel is hosted by Shawn, who's all too happy to remind the viewers where they'll go after they die.
When juggling the Earth-destroying detonator during the filming of "You've Changed, Man", Manny Jacinto accidentally lets it fall. The cast reactions have to be seen: Kristen walks around in stunned silence, Will and Ted scream and run, D'Arcy bounces from wall to wall, Jameela straight up faints, Marc Evan moves in slo-mo and Maya starts scream-laughing like a banshee before chanting "I saw it coming!".