Ronin, the Ender

Indestructible
Whenever Ronin attacks, you may pay {b}. If you do, destroy target permanent.
Whenever Ronin blocks, you may pay {w}. If you do, destroy target permanent.
If Ronin were to enter a graveyard, exile it instead.
He was disturbed from his journey of solitude. He will not rest until his committal has ended.