Siege of Boralus

Whenever a creature you control attacks, put a Cannonball counter on Siege of Boralus.
Creatures you control have haste as long as Siege
of Boralus has five or more Cannonball counters
on it.
At the start of your turn, you can destroy Siege of Boralus and pay X mana, where X is the number
of Cannonballs. If you do, destroy target creature
or planeswalker an opponent controls with
converted mana cost X.