When Lucy and Gru are reviewing Paradise Mall shop owners (suspects), the owner of Stuff-A-Bear (a satire of Build-A-Bear) overstuffs a bear and it explodes, making an expectant little boy cry. The boy is the same one that Gru made cry with a popping balloon in the beginning of the first Despicable Me (2010).
When Lucy Wilde gives Gru a phone number to reach her, it is clearly visible as 626-584-5723. Calling that number reaches a recording of Kristen Wiig in character, with her outgoing voice mail message. However, the voicemail box is full, and you cannot hear her recording.
El Macho drinks a liquor bottle during a flashback scene. The label says "La Venganza del Escorpión", which is Spanish for "The Revenge of the Scorpion". Behind it there is a poster, also in Spanish, that reads "If you are drinking to forget, pay first."
The actors are filmed the entire time they read their parts. Their facial and hand expressions are used on screen. Steve Carell's wife had fun pointing out the expressions in Gru that reminded her of Steve.
The start of the film features yellow-jacketed humans speaking a foreign language. This is a reference to the original design for Despicable Me (2010)'s minions - the iconic shortened shape came about as a result of a low budget for the first film.
When Gru first visits his Minions in the underground workshop, several Minions can be seen taking a break and eating lunch on top of a cross beam. This is an homage to the famous "Lunch atop a Skyscraper" photograph from 1932.
When Silas Ramsbottom shows Gru a video of a rabbit being injected with mutation serum, the name tag of the scientists in the video read "COFFIN" and "RENAUD" - a reference to directors Pierre Coffin and Christopher Renaud.
When the Minions assemble to give Dr. Nefario a 21-fart-gun salute, the bugle call "To the Color" can be heard playing in the background. This is a U.S. Army bugle call that is traditionally played on Army posts after the call of "Retreat," as the post flag is lowered at the end of the duty day.
There's a brief shot in the film in which Edith is playing ping pong with a minion, but uses a pair of nunchaku as opposed to a ping pong paddle. This is a reference to a famous Chinese Nokia commercial in which a Bruce Lee impersonator in a mock "lost home video" also plays a game of ping pong using only a pair of nunchaku.
The 626 area code is from California, meaning that this movie and the original Despicable Me movie probably take place in the San Gabriel Valley or nearby in the northeast portion of Los Angeles county.
When the minion with the Popsicle wakes up on the island, he looks around and then heads to the beach. When you look toward the water, there is a green "El Macho" flag visible in the sand on the left side.
Near the end of the film when Gru is fighting the infected minions an air ship controlled by Margo, Edith, Agnes and Dr. Nefario can be seen. The ship looks oddly familiar to the clone dropships found with Star Wars Attack Of The Clones.
When Gru takes off on his motorcycle (shades of James Bond) to rescue Lucy, he's wearing a helmet with goggles. The directors didn't want to show him wearing the goggles, because he would look like a Minion; plus, it's a throwback to various World War II movies where a hero rides a motorcycle.
At Agnes' birthday party at the beginning of the movie, some kids are playing a fishing game in a small kiddie pool. One kid hooks a piranha that looks just like the ones in Vector's piranha gun in the first movie.
When Gru enters the Eagle Hair Club and Eagle-san greets him, Eagle-san is petting what appears to be a long-haired white cat (which actually turns out to be a wig). This is a reference to James Bond films in which the leader of SPECTRE is petting a white cat.
The scene in which the transformed Minions are boarding the rocket ships has a shot looking over El Macho's shoulder as he surveys his army. This is a reference to a similar shot in Star Wars Episode II: Attack of the Clones, where several Jedi leaders survey the Clone Army boarding their transport ships.
In Despicable Me (2013), Gru (Steve Carell) is a single dad with three orphaned daughters, one of whom - Margo - is 'dating' a young boy, which Gru is trying to prevent from dating. In a previous film, Dan in Real Life (2007), Dan (Steve Carell) also plays a single (widower) dad with three daughters, one of whom - Cara - is also 'dating' a young boy, which Dan is trying to prevent from dating. Interestingly, both of the young boys are Spanish-speaking.
This is the second time we find a Kristen Wiig character in a cupcake bakery. In this film, she has a scene with Gru in "Bake My Day". In Bridesmaids (2011) she used to own "Cake Baby"* bakery where she made cupcakes.
The trivia items below may give away important plot points.
One of the minions in the end credits has Heterochromia iridum. His left eye is brown while his right eye is green. This is Bob, one of the minions in the upcoming film Minions(2015) about how the minions met their boss.
At the wedding the minions singing "I Swear" were modelled to resemble the singing group Boyz II Men, however, the R&B group that originally recorded the song was All-4-One. Boyz II Men never recorded it.
After Gru pretends to be captured and enters the castle, one of the minions gets his purple covering smudged and one of the mutant minions points at him and screams - this is a reference to the end of the "Invasion of the body snatchers" film.
Gru seems to be very wealthy, as indicated that he pays each of the minions wages, and there are over 10,000 minions. Although, it is also indicated that much of his money comes from the Bank. However, his source of income in Despicable Me 2 is still unknown.
Whenever the Lipstick-Taser is tasing a person, It is noticed that the person dances rapidly fast. For example, when Lucy tases Gru he dances with his finger up and down and when Gru tases Eduardo/El-Macho he seems to be first dancing with a guitar then dancing with his hands over the waist before falling down.
When Gru enters El Macho's fortress as a 'prisoner', he says, "Curses, foiled again!" That is the catch-phrase of Snidely Whiplash from the 'Dudley Do-Right of the Mounties' cartoon, and has been used by various other villains in other cartoons.