Growth
increases your Pokémon's Special statistic by an amount equal to one-half
of its initial value. Thus, the first use of this attack results in 150%
normal Special. The second use results in double the normal Special score,
and so on. Effects are cumulative for a maximum of 6 uses, at which point
your Pokémon's Special will have reached quadruple the normal value.
Further uses will have no effect.
Note that like other statistics, Special has a maximum value of 999. If
a use of this attack would raise your Pokémon's Special beyond 999, it
will instead raise it only to that value. If its Special has already
reached 999, this attack will fail.
Also note that since the attacker's Special statistic is being altered,
both the effectiveness of the attacker's Special attacks and resistance to
such attacks, such as Bubblebeam and Vine Whip, will be increased.
Damage caused by and resistance to Physical attacks like Pin Missile and Jump Kick will not be affected.
For more information on the different kinds of attacks and how damage
is determined for each of them, see the Attack Base Explanation.