Kyra Sedgewick plays a Deputy Chief sent to evaluate the 99, just like she played Deputy Chief Johnson in The Closer. She even has a rivalry with another straight-laced cop. At least she's using her actual accent this time.
Luis Moncada plays Tito Ruiz, the Giggle Pig kingpin, and is wearing the exact same suit he wore on Breaking Bad where he played Marco Salamanca, another menacing guy involved in the drug trade. As a bonus, Jake is very obviously dressed up like Jesse Pinkman in the same scene.
Terry is a talented artist. Terry Crews originally went to university on an art scholarship before earning a spot on his school's football team and going onto the NFL.
The Funeral guest stars Archie Panjabi as a member of the legal system who wants casual sex with a cop. Though this time she's a cop instead of a former investigator for the DA's office.
Actor-Shared Background: In "The Apartment", Gina and Jake reference being friends since they were kids and hanging out together. Andy Samberg and Chelsea Peretti, who play Jake and Gina, have actually known each other since they were kids.
Casting Gag: This isn't the first time that Andre Braugher has played an uber-serious and imposing police officer. But unlike the grim and gritty environment of urban realism that Detective Frank Pembleton starred in, Captain Ray Holt operates in a comedic setting populated by goofy eccentrics. On top of that, Frank Pembleton was the brilliant-but-arrogant lone-wolf cop who refused to play with others and had to be pressured into doing so by his commanding officer. In Brooklyn Nine-Nine, Ray Holt is the commanding officer who has to deal with an arrogant lone-wolf detective who refuses to play with others and has to be pressured into doing so (Peralta). And to finish the gag off, on the earlier show Braugher played the partner of a detective who eventually came out as bisexual, while in this show he plays an openly gay police officer.
The Cast Showoff: That is Scully singing opera. Joel McKinnon Miller, the actor who plays him, took opera singing lessons in his youth.
Celebrity Paradox: Saturday Night Live, which had B99 star Andy Samberg on it for several years, apparently exists in this world, and Peralta even interacts with Adam Sandler...who apparently doesn't notice how much the detective resembles his That's My Boy co-star.
Dawson Casting: Inverted; while his age has never been specified Captain Holt is old enough to have been an active (albeit fairly young) detective in 1979. Andre Braugher, the actor who plays him, would have been 17 at the time.
Andy Samberg is older than his character by 3-4 years.
Hide Your Pregnancy: Played with regarding Melissa Fumero's pregnancy in the third season, in which the producers seem to enjoy bouncing between covering it up, pretending that she's not visibly pregnant, and lampshading the hell out of it at every opportunity. By the last three episodes, they end up dealing with the situation by having Santiago go undercover in a prison... as a pregnant woman.