Pretty much sums it from the canon page. Some people who write fictional works or make games or films try to be careful with their canon. Mistakes will always happen, though,
- Character appearing out of no place. When they first appeared, it explains how they got there.
- Character pasts, injuries and other stuff.
- Location hops. How did character A get to place B so fast?
- How did character A befirend character B when character C rescued or saved them?