Perfect shot

(You may only cast a legendary instant if you control
a legendary creature or planeswalker.)
Destroy Target creature.
It can't be regenerated.
Its controller loses life equal to its mana cost.
"As she returned from the portal I looked into the
eyes of a soulless machine who had lost sight of who
she truly was and knew that there was no hope in
stopping her, but at least I can get in one last..."