Outside of battle Flash may be used to light up dark caves.
Flash will lower the opponent's Accuracy by 1 step on the standard Accuracy scale.
Flash will always fail if it has already been used 6 times on the same pokemon, without a move that raises Accuracy being used by or against the pokemon affected by Flash. This is due to the fact that a stat may only be lowered by a maximum of 6 steps, until it is reset by the use of Haze or the pokemon is switched out normally. The maximum is the limit of how many decreases can be applied to a stat. If another move decreases the Accuracy stat of the pokemon that Flash is used against, the number of steps that it decreases the Accuracy stat by will count toward the 6 step limit, and reduce the number of times that Flash can be used appropriately.
Flash is affected by Brightpowder when the opposing pokémon is equipped with it. Now there's some irony for 'ya.