Supernatural season 10 midseason Finale
Screen shot of Supernatural season 10 midseason finale shows Dean covered in blood and surrounded by bodies.YoutubeScreenshot/The CW

Supernatural mid-season finale left us with a dark Dean, who is out for more blood when the season returns.

Dean had been struggling with his Mark of Cain in the last few episodes, but he finally gave in to the dark temptations in the mid-season finale.

Episode 10 titled, The Things We Left Behind started slow, and had a more intimate storyline. It did not include fighting any monsters, but involved fighting internal demons.

For Castiel that meant revisiting his vessel's daughter, Claire, whom we last saw in Season 4'.

Castiel, wanting to improve his relationship with his daughter, makes Sam and Dean reminisce about their father, John Winchester and they take a little trip down memory lane.

Watch Supernatural season 10 mid-season finale online

But slowly and gradually the fall finale episode built up to a simmering conclusion, and set the stage for Dean's slow descent into madness.

The episode begins with Dean having visions of a bloodied house, where he butchered a group of people with a knife, and by the end it became a horrific reality. Sam stands there aghast and horrified at his brother's descend into darkness.

What will happen when the series returns?

The next episode which will air on January 20th, 2015 is titled, The Hunter Games where Dean will be out for Metatron, who is responsible for making him a demon, and killing and punching whoever tries to stop him.

As previewed, the season is the 'year of the Deanmon', and episode 11 might actually brings us back to the subject of Dean and Demon.

By the looks of the promo, the Knight of Hell is just as dark as ever.

The promo titled, Born Killer, shows Metatron held as a prisoner, strapped with chains to a chair.

Metatron says about Dean: "Full-out, foaming-at-the-mouth maniac. He's gone nuclear."

Then the shot cuts to a slew of scenes featuring Dean punching Charlie and Metatron.

"There is the Dean I love," says Charlie.

The promo also shows Castiel and Sam trying to stop the elder Winchester, and Crowley, the king of Hell is not in a good condition.

Charlie (Felicia Day), who fans last saw in season 9, will be making her return from Oz to the real world. Meanwhile, Metatron will pay for killing Dean in the season 9 finale, which resulted in him becoming a demon.

According to a report in Eonline, fans will finally get to see the long-awaited return of Cain in the 2nd half of season 10.

Tim Omundson plays Cain of the biblical story of Cain and Abel. He was first introduced to the CW show last season in the episode, First Born, where Cain passed off his mark to Dean, giving him the ability to wield the blade.

Omundson tweeted his return to the hit CW series

Maybe Cain's return is good news, as he might help Sam take the mark back from Dean.

Watch the promo of Dean going nuclear here: