Shout Out / Avengers: Endgame

• Tony cheekily compares Nebula to a "Blue Meanie" from The Beatles Animated Movie Yellow Submarine in his recorded will to Pepper (in the French version, he calls her the Smurfette instead). He refers to Ant-Man as Thumbelina and Stuart Little. He also snarkily calls Thor (after five years of letting himself go and drinking like crazy) "Lebowski".
• When Bruce and Rocket visit Thor in New Asgard, the latter initially thinks that it's someone to fix the cable. In The Big Lebowski there's a scene in which the titular character, whom Thor now resembles, watches and discusses the intro of an adult movie where the male actor states that he's there to fix the cable.
• Thor's roommates Miek and Korg are playing Fortnite.
• The grand plan to jump back in time and snatch the Infinity Stones is referred to as a "Time Heist".
• The cast mentions multiple Time Travel works while planning the Time Heist, including Back to the Future, Star Trek, Bill & Ted's Excellent Adventure, The Terminator, Timecop, A Wrinkle in Time (specifically the sequel books, but that's not mentioned), Somewhere in Time, Quantum Leap, Hot Tub Time Machine and Die Hard, only for Scott to remember that the last one isn't actually a time-travel movie.
  • Furthermore, whilst Avengers: Endgame goes to great lengths to lampshade that time travel does not work in the same way, the plot of the movie (particularly during the second act) borrows elements liberally from Back to the Future Part II: both films revolve around the heroes having to go back to events and locations from the past that are connected to them, to retrieve one or more MacGuffins, encountering and avoiding their past selves or (in Thor and Tony's cases) their parents, in order to thwart a Bad Future caused by said MacGuffin(s) falling into the hands of the Big Bad, and a younger iteration of said Big Bad acting as a Spanner in the Works in the finale.
    • Both movies also conclude with a main character getting sent back in time - one (Doc Brown) being accidental, the other (Steve Rogers) on purpose - which leads indirectly to them getting a Happy Ending with the love of their lives.
• When Tony checks on Rocket's repair work leading up to the Time Heist, he calls him "Ratchet", to which Rocket annoyingly replies "It's Rocket, not Ratchet!". Both are small, fuzzy, gun-toting aliens with an itchy trigger finger. Naturally, Insomniac Games ran with it and put up a "Ratchet, not Rocket" shirt on their store.
• Rhodey warns Nebula about there may be traps in the vault housing the Orb/Power Stone. There weren't any (aside from the shield around the Orb), but the traps that he thought of are lifted from Raiders of the Lost Ark.
• Nebula, after reaching through the energy shield guarding the Power Stone, melts the synthetic flesh off her right arm, which now bears an exact resemblance to the T-800's metal endoskeleton arm from Terminator 2: Judgment Day. That scene is also similar to I, Robot where Sonny reaches into a forcefield to obtain the nanites needed to kill the Big Bad.
• Joe Russo revealed in an Empire podcast episode that the scene where Thanos sits talking on a stump while Tony, Steve and Thor approach is an homage to Once Upon a Time in the West.
• Thanos's double-bladed sword, which can be hurled like a giant shuriken/buzzsaw through his enemies and then returns to his hand on command, resembles and functions almost exactly like the similar sword wielded by Tessai the rock-monster from the 1993 anime classic Ninja Scroll.
• Iron Man being the one to deliver the finishing blow against Thanos may be a reference to the fact that the villain's first appearance was in an Iron Man comic book.
• The animation of the Leviathan about to devour Rocket right before getting turned to dust by Tony's snap looks exactly like the animation of the holographic Jaws advertisement attacking Marty in Back to the Future Part II.
• To Star Trek:
  • Kevin Feige cites the Star Trek: The Next Generation series finale "All Good Things..." as an inspiration for the five-year Time Skip, allowing us a glimpse into the future. That finale is also a Time Travel Episode allowing the show to revisit, re-live and (occasionally) revise past triumphs, much as this film does.
  • In an interview with SModcast, writers Markus and McFeely revealed that the credits with the signatures of the original six Avengers is inspired by the credits of Star Trek VI: The Undiscovered Country.