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Supernatural season 9 finale episode titled 'Do You Believe in Miracles?' will air on 20 May and it promises to be quite a shocker.

Here's a preview of the episode (via

The final episode of this season will see Dean feeling the effects of the First Blade. Meanwhile, Sam, Dean and Castiel face shocking consequences when they take the fight to Metatron, who makes his move against humanity.

The 'Do You Believe in Miracles' preview video shows Dean struggling with the effects of the Mark of Cain. We've seen what it's been doing to him, but how far is he going to go in the finale? Will Sam be able to get through to him before it's too late?

"I get this high, and I want to kill," Dean says. "It's the mark," Crowley explains. "The more you kill, the better you feel."

Will Dean kill Metatron? If he does, what will be the cost?

Supernatural season 9 finale episode airs Tuesday (20 May) at 9 pm on CBS.

You can click here to watch the episode online.