The season 12 finale of The CW's seemingly immortal series Supernatural posits an interesting question of which is the bigger threat: The British Men of Letters, a recently repowered Lucifer, or his unborn child whose whereabouts are currently unknown after Castiel absconded with the very pregnant Kelly Kline. It's building up to one of the series' most personal conclusions, as this season not only brought back Mark Pellegrino as Lucifer, but it also introduced Sam and Dean to the mother that was lost to them when they were just children. And with the revelation that she'd been brainwashed by the British Men of Letters and compelled to do their bidding – which entailed locking her sons in their bunker with a limited air supply – it stands to reason that the brothers will have all sorts of new and interesting emotional baggage to choke down like so many bar burgers lest it get in the way of slaying monsters.

Now that Riverdale is out of the way, Supernatural can step up to the plate with a two-hour finale – that is really just the final two episodes of the season in one block – which is odd, considering it puts the series a week ahead of the finales for Arrow, The Flash, and Supergirl. While that might make some question why the show is ending its season a week ahead of the network's other high-profile offerings, it does allow for the show to go out big for the season – at least in terms of the size of its finale.

And what a finale it was. The CW was smart to package the two installments in one shot, as 'Who We Are' wouldn't have been nearly as effective a penultimate episode if the potentially revelatory 'Along the Watchtower' didn't immediately follow it up. A lot that has to do with certain smart choices that were made in breaking the season, as the writers wisely split the overarching narrative up between the encroaching threat of Lucifer – brought to obnoxious, self-satisfied (and funny) life as only Pellegrino can play him – his unborn child, and the more present problem of Ketch and the British Men of Letters' growing brand of authoritarianism.

That essentially necessitated the existence of two endings for the season, otherwise the finale would have felt even more rushed than it already did, meaning 'Who We Are' acted as the emotional apex for season 12, as Dean manages to find some release in his complicated feelings toward Mary while Dean takes down a wing of the BML with the help of some flannel-clad hunters. The latter manages to set up a confrontation between the Winchesters and their old buddy Lucifer. And while it's to the final hour's advantage that Ketch and the British Men of Letters are officially (though probably temporarily) off the board by the time 'Along the Watchtower' begins, the episode has so many surprises in store for the audience that there's precious little time for any direct conflict between Lucifer and the Winchesters.

That may have been one of the bigger issues with season 12 overall: Lucifer is such an enormous threat that the only way the audience can buy his continued presence amongst those in the land of the living is if he's dealing primarily with someone whose power levels at least give them a fighting chance. So once they did away with Rick Springfield as the vessel for the archangel, Pellegrino spent most of his time on screen bantering with and then smacking around Mark Sheppard's Crowley. That kind of interplay certainly has its advantages, but given the personal connection Lucifer and Sam share, reducing their interaction with one another to a phone call and a quick standoff was a bit of a letdown.

Instead, 'Along the Watchtower' hedged its bets that a quick succession of surprises would outweigh the lack of meaningful interaction between enemies who know each other all too well. Kelly's labor brought about a tear in the fabric of reality, opening a portal to another dimension in which the Sam and Dean were never born, and the world was plunged into a never-ending war between heaven and hell. The only upshot to the dreary place strewn with dead bodies is that Bobby Singer (Jim Beaver) is alive in that reality. He's taken up angel killing as a hobby and has donned a very fashionable beret as part of his apocalyptic ensemble.

Though it's a fun cameo for Beaver that again underlines just how much history there is for the writers to dig into each new season, Bobby's appearance is as much a matter of narrative necessity as the inexplicable tear in the fabric of reality. The latter sets up a convenient solution to the Lucifer problem, one that's dealt with on the fly and that facilitates two honestly surprising deaths that could well have major ramifications for the series moving into season 13 – or it could all be undone because, you know, there's a magically mature newborn hanging out in the corner of a surprisingly well-appointed nursery who can apparently open up doors to another dimension just by being born.

Still, that doesn't necessarily lessen the immediate surprise of Crowley's sacrifice, or of Castiel being killed after believing he'd successfully dispatched the devil. It speaks to the continued appeal of Supernatural that the show can ax two major players like that – after killing off the show's actual protagonists time and time again – and have it land with the sort of force it does. While Castiel's death stands to mean more to the show's fan base, Crowley's suicide came on the heels of his admitting he never really wanted to rule hell – or that he really hated his job once he'd gotten it. Sure, his actions were drastic, but for anyone who's ever attained a position they thought they wanted, only to have it ruined by the obsessive neediness of others, you can kind of see why the demon felt this was the best way to stick it to Lucifer.

Add the death of Crowley and Castiel to Mary being pulled into Bobby's World by Lucifer and you have all the ingredients for one of the most somber and personal endings on Supernatural in a while. After so many seasons have ended with the supposed death of either Dean or Sam, it's refreshing to see them dealing with the fallout of the lives they lead and the sacrifices that so often have to be made in the pursuit of saving the world. If there's a sliver lining to the rather dark cloud that is 'Along the Watchtower', it's that the dimension in which the brothers Winchester never existed stands as proof of just how important they are and continue to be. Whether or not proof of their importance now includes co-parenting the Devil's child in season 13 remains to be seen.

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Supernatural will return for season 13 in the fall of 2017 on The CW.