Change your preferences here.
Deals damage. The target's Defense stat, and not its Special Defense, is used in damage calculation. All other factors work as expected.
This move is pretty much what makes Mewtwo the absolute horror that it is, especially compared to the previous three generations when Psychic resistances were more prevalent and Mewtwo had to use Taunt or physical attacks to have any hope to get past Blissey. Thanks to Psystrike, Mewtwo can be, for most intents and purposes, a mixed attacker without compromising its huge base 154 Special Attack in the slightest. Combined with its high Speed, Mewtwo has a significant advantage in Calm Mind wars due to Psystrike hitting the opponent on its unboosted Defense stat. It is also a powerful enough move to be a significant threat on defensive Mewtwo sets.
Psyshock is an equivalent with 80 Base Power.
Psychic is an option with 90 Base Power that does not target the foe's Defense.