Supernatural Season 10 Spoilers: Extended Promo for Midseason Finale 'The Things We Left Behind'

Supernatural will air its Season 10 midseason finale, "The Things We Left Behind," on Tuesday, and a new extended promo shows just how bad the situation gets for Dean with regard to the Mark of Cain.

Check out the clip below, in which Dean makes Castiel promise to kill him if the Mark makes him bloodthirsty again.

In case you missed it, here's some of what we had to say about the most recent Supernatural episode, "Hibbing 911."

"It was an interesting twist on vampires, which Supernatural has done to death and beyond at this point. But the entire episode just had that feeling that too many Supernatural episodes have these days. It happened, it was largely irrelevant to the main plot, and now we move onto next week. We got a brief tease at the end (as we always do) with regard to the season-long arc, as Dean said he didn't feel like the Mark of Cain was driving him when he killed the vampires. Of course, this is Supernatural, so things are going to go south in a hurry here.

The episode also established some continuity with two of the more forgettable episodes in the series: Jody's adventures with the vampires from late in Season 9 and Sam and Dean's journey to the weight loss clinic in the middle of Season 9. Both of those were largely forgettable installments, but it was good of the show to keep the minor details in focus.

It was pretty funny to see Donna react to the knowledge that monsters are real, but she took it all in stride. The show almost treats these reveals as a joke now, as Donna learned everything off screen and all we got was a simple, 'We good?' from Dean to confirm that she was on board.

Next week is the midseason finale, and the previews at the end of the episode teased that the Mark of Cain would be in full effect. Dean was standing in a room bathed in blood, so here's hoping the episode ends 2014 on a high note for Supernatural."

What do you think of the clip? Let us know in the comments section.