Witch Engine

{5}{B} · Creature — Horror

Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.) {T}: Add {B}{B}{B}{B}. Target opponent gains control of this creature. (Activate only as an instant.)

Motor: se resuelve a mano

Rulings (1)

Because the ability is targeted, it is not a mana ability. It can only be activated when you have priority, and goes on the stack like other non-mana abilities.
Wizards of the Coast · 2008-04-01