Blood Cannon

Whenever a creature dies, put a blood counter on
Blood Cannon.
{5}{b}{b}{r}{t}: Blood Cannon deals X damage to X targets. X is the number of blood counters on
Blood Cannon. Remove that many blood counters.
If a creature is damaged/dies by this effect, put a
death mark on that creature.
If a creature with a death mark leaves/enters the graveyard, exile Blood Cannon. This cannot be prevented.