Supernatural, on The WB (s1) / The CW (s2-15)
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Caution: Oh! So! Very! Many! Spoilers! (someday)
So, what happened when the Mark of Cain was removed from Dean was that something called "the Darkness" was released. When that happened, Dean met the Darkness, in the form of a woman named Amara, who believes the two of them are now bonded, since he was the one that released her. But their meeting took place... I don't know, on like a different plane of existence, or something, and it was very brief, before Dean reappeared on Earth, and reunited with Sam. After that, Amara is born as a baby. And over the next several episodes, she'll grow by leaps and bounds, so we see her at at a few different ages, before she finally appears the same age as when Dean first met her. For awhile, Crowley has young Amara locked up, while trying to gain her loyalty so that he can eventually use her. But she consumes various demon souls, which makes her stronger. Eventually she leaves, and starts consuming human souls. Meanwhile, a couple of angels kill Hannah, after which I guess various factions will vie for control of Heaven. But eventually the factions will come together, because they realize they need to be united to stand a chance against Amara. (Various low level demons and angels had previously realized the same thing.) Meanwhile, Sam begins getting visions of the Cage in Hell where Lucifer is locked up (and where Sam himself had been trapped, between seasons 5 and 6), and he believes the visions are a message from God. He eventually gets the idea that God wants him to go back to the Cage, though of course Dean is totally against that idea. Also, Castiel tracks down Metatron and retrieves the demon tablet from him. (Metatron is human now, and I have no recollection of that happening.) And of course, as always, there are standalone jobs for Sam and Dean to work as Hunters, whenever they're not trying to track down Amara or figure out how to deal with her. (I really enjoyed the episode with imaginary friends, including one named Sully, played by Nate Torrence.) Anyway... we eventually learn that Amara is God's sister, and once she reaches her full strength, she'll be just as powerful as he is. She wants to find him and get revenge for locking her away eons ago, but as usual, he's nowhere to be found. Meanwhile, Sam and Dean finally enlist the help of Crowley and Rowena to contact Lucifer and ask for his help against Amara. However, when he asks that Sam invite him to use Sam as his vessel, Sam refuses. But then, somehow, Sam ends up back in the Cage, at Lucifer's mercy (or lack thereof). And Lucifer tells him something I'd suspected pretty much from the beginning, but I won't spoil that just yet....
Unfortunately, after the midseason break I had to stop watching the show, so I don't know when I'll be able to continue updating the review.
Carry on, my wayward son....