When first watching this episode, I had a mixed reaction to Into the Mystic. At first appearance this was one of those episodes that was all about character - less about plot.
The characters, including the guest characters down to the smaller appearance roles, were by and large well developed and enjoyable characters. Sam and Dean had some enrichment and breathing room after a few big blows in recent weeks and even confronted a few metaphorical demons along the way. As far as the plot went? Well, frankly the banshee wasn't much to talk about. Then, on rewatch there was one, small thing about the entire plot that caught my eye and made it seem all the more significant in retrospect.
Casifer/Lustiel
As I mentioned above, the characters have the richest material to pluck from this episode, on a primary, character level rather than a story level. Lucifer as Castiel didn't really do much this week but boy, was he fun to watch. That was my initial opinion and it stands today. Misha must have had a ball relaxing the Castiel character for the more swashbuckling Lucifer. The encounter with prowler angel in the park was interesting - though why this guy though he'd be able to take on an Arch-Angel alone is anyone's guess. Lucifer is clear and legitimately enjoying his time above ground, what with the leaf plucking and playground watching. 
One of the best parts of this new incarnation are the expressions that we the audience are privy to unbeknownst to, in particular in this episode, Dean. Castiel's mildly irritated look on being discovered by Dean in the bunker reminds me of how I feel when a client asks me an absolutely ridiculous question I've answered twice already and I need to smile and answer a third time, kindly and without condescension. Yes, I can relate to and enjoy Lucifer in Cas' form for a while - even if the boys' ignorance made for anxious viewing the longer it went on (I’m an immersive viewer that way).

The Banshee: Underwhelming
This was one of the most visually lackluster villains in Supernatural history. There - I feel better. As CGI conceptions go in the year 2016, this was disappointing. In the early days of SPN, maybe she would have been passable, sure, but today she was entirely fake and this distracted. Having said that, the villain wasn't really much more than background noise (if you'll excuse the pun) in this episode. The banshee could easily have been substituted for any other beastie to the same effect, for the most part.
Mildred & Aileen

Aileen, for her part, was even more unique in her connection to the Winchesters and the Men of Letters. The episode opens with the banshee killing two people in Cork, Ireland and a small baby left crying in her crib. This, we learn, was Aileen and her mother was the daughter of a Men of Letters. Very briefly Dean references that Aileen’s grandfather was part of a small faction of MoL sent to Europe.
This tiny piece of information didn’t mean anything on the initial viewing – but of course on the second watch after learning of the UK MoL branch who’ve sent people to take care of Sam and Dean? Was this an allusion to what was to come?
Both Aileen and Mildred were strong and independent characters who took care of themselves well and between them managed to save Dean from the banshee rather than be saved themselves. Although Aileen didn’t find any particular closure from the act – both she and Mildred agreed watching Sam and Dean walk away was a great treat.
Brother Moments
As with the season, 11.11 continued to be ripe with the brothers exchanging honesty (for the most part) and classic scenes of the boys together. A salt and burn, be it ever so simple or unnecessary as was the case here, still offers characteristic visuals of Sam and Dean’s faces against the flames and the opportunity to talk in the dark while having a beer. Sam didn’t take the conversation chance here, but later confessed to Dean his experience with Lucifer in the Cage and overwhelming guilt he was carrying still which gave the opportunity to finally wipe the slate clean about anything that may be between them from past sins:
“All that matters, all that’s ever mattered, is that we’re together.”

Retrospective Thoughts
Great, smiling episode with a weak monster. 11.11 stands easily on its own or as part of the flow of season eleven and is a perfect character driven episode. The banshee is a disappointing though minimal piece of the plot and doesn’t affect the overall quality of the episode. Strong writing and the humour from our actors is excellent. Plus, the nuggets that may or may not be hints at the end? Worth watching just to be discovered.
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