Character mistake: The sign for the hotel where Jake is staying at in Mexico says Tengo Quarto's para Renta. The word is spelled wrong. It should say CUARTOS. Also, there is no apostrophe s in cuartos. It is plural, not possessive.
Character mistake: Clark has too many lights on his house causing the city to go dark. There is a scene where the power plant needs to boost their output. There is a close-up of a guy flipping the switch. Look at the way they spelled auxiliary - auxilliary. (00:37:54)
Character mistake: In the finals of Video Armaggeddon the compere keeps making comments such as "Jimmy loses a life and starts over in world two", "Laura finishes world two", "Lucas finishes world two". All three times the relevant person is actually in World 1 - Level 3. In Fact at no point are any of the competitors in World 2 and the only time any of them is out of World 1 is when Jimmy uses the warp to access World 4.
Character mistake: While pitching his shrinking machine to NASA Szalinski claims that reducing the size of a rocket's payload would result in "staggering" savings in the fuel required at takeoff. However, he makes it clear that his machine works by reducing the space between atoms, meaning that the shrunken object weighs the same as the original. Weight is the critical factor in calculating fuel consumption, not size. Anyone at NASA would pick up on that instantly.
Character mistake: In the movie they grab Genghis Khan in 1209 which would have been correct, he ruled Mongolia from 1206 to 1227. In the presentation at the end they say in 1269 he did this and that, that would have been Kublai Khan's reighn of terror in Mongolia.
Suggested correction: Bill and Ted have proven not to be that smart. Easy for them to get those things confused.
Character mistake: At the psychiatric ward, Ray says that Vigo is a XVII century tyrant; it's not a very fitting way to describe him, since he saw the XVII century for just a decade; as the book mentioned, he lived from 1505 to 1610 and was the scourge of Carpathia for the XVI century. (01:16:15)
Suggested correction: Not a mistake, Vigo was a tyrant in the 16th and 17th centuries, Ray chose to label him a 17th century tyrant because that's the century he died in. It would be like calling Osama bin Laden a 21st century terrorist, which is correct, even though he also committed terrorist acts in the 20th century.
Character mistake: Dooley refers to his car several times, saying "my 1965 Mustang." It is actually a 1966 Mustang.
Character mistake: When Mollie goes to Albert's office for the first time since having Mickey, Albert asks if he is walking yet, and she says no. In the next scene with Mickey, he walks, and is walking when he visits Albert's office.