Tail Whip will lower the opponent's Defense by 1 step (termed BTLs in the Gameboy description) on the Stat growth scale.
Tail Whip will always fail if it has already been used 6 times on the same pokemon, without a move that raises Defense being used by or against the pokemon affected by Tail Whip. 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 Defense stat of the pokemon that Tail Whip is used against, the number of steps that it decreases the Defense stat by will count toward the 6 step limit, and reduce the number of times that Tail Whip can be used appropriately.
Tail Whip is affected by Brightpowder when the opposing pokémon is equipped with it.
