Leyline of the Doomed

If Leyline of the Doomed is in your opening hand, you may begin the game with it on the battlefield
under an opponents control.
When Leyline of the Doomed enters the battlefield, choose a creature type. Creatures you
control are the chosen type.
{1}{b}{b}: Put a -1/-1 counter on all creatures of the chosen type. Only the owner of this card may activate this ability.