Factual error: The video games Operation Wolf and Rampage were visible in the Family Amusement Center arcade during the opening. However, this would not be possible during the movie's 1984 setting since Rampage wasn't released until 1986 and Operation Wolf wasn't released until 1987. (00:12:48)
Factual error: The old percussion double barrel shotgun is firing modern shotgun shells, which would never work or fit in that gun, and furthermore are also made of plastic, wrong for the era.
Factual error: The plot's main conceit hinges upon coders, the art department, and the user-end network team constantly working live at the same time in the same room, as well as developers actively writing code, rebooting servers, and chasing players in-game to get rid of problematic players. No real game company could operate this way. Game content patches wouldn't change the network experience, and in-game aesthetic changes like the ones they make in seconds would require weeks if not months of development.
Factual error: When John Thornton is in the bar, Hal comes up and punches him in the face. They fight and argue, and Thornton proceeds to say that Hal "sucker punched" him. However, the term sucker punch was first known to be used in 1926 while Call of the Wild was published in 1903. The story itself took place in the 1890s.
Factual error: When "some Frida Kahlo-looking asshole" is chasing Harley across the bridge during her close-up you can see that the cartridges are loaded backwards into the cylinder. (00:54:05)
Factual error: Not only Mulan's horse is able to outrun an avalanche (at the beginning even unseen by the large enemy army who does not even notice the event occurring), but it also gallops through it undisturbed while Honghui is being carried away depicted as being in serious danger. (01:09:30)
Suggested correction: This is consistent with what you see throughout the whole film: Mulan consistently breaks the laws of physics because her "Chi" is strong. (Translating it to the Star Wars lingo: Strong with her The Force is.) Five minutes before (video time, not in-film time) she reversed the flight direction of a spear. This is a fantasy film and is supposed to do all of this; we watch it knowing that magic, "Chi", and The Force are not real.
That's a composition fallacy.
Factual error: Real-life Martina Franca is a town in Puglia, at the "heel of the Italian boot." The town shown in the film is the famous San Gimignano in Tuscany. And when Holly "defects" in order to go to the Hill of Tara, her departure point, as seen on Foaly's observation monitor, is the real-life location of San Gimignano. (00:35:50)
Factual error: Joel is using a ham radio set to contact his old colony. A shot of the radio set shows it is set to "CW", which is Morse Code, but he is using voice. And the strength meter is on zero. It should be showing the signal strength. (01:24:00)