When a Pokemon has an ability that changes their normal moves to another move, e.g. Refrigerate, moves like Tackle, Return, Take Down etc. will hit Ghost types as an Ice move, or whatever type the move was changed to. Obviously, if the move was changed to something that Ghost types are immune to, e.g. Fighting, then the move would have no effect.
Scrappy also allows Normal and Fighting moves to hit Ghosts, but it doesn't change the type of those moves.