We all know that Judgment is a Normal type move, and Normal type moves have no effect on Ghost type opponents. But, if I make Arceus hold a Dread Plate and then make him use Judgment against a Ghost type opponent, will it hit the target?
Judgment inflicts damage and has no secondary effect. The type of Judgment depends on the type of Plate held by the user, being Normal-type if there is no held Plate.
Source
Boosts the power of the holder's Dark-type moves by 20%. If the holder uses Judgment, it becomes a Dark-type move.
Because of this, Judgement would become Dark-type if it holds Dread Plate, and therefore, be able to hit a ghost-type super effectively.
Hope this helps!