For a player's life total to become 10, what actually happens is that the player gains or loses the appropriate amount of life. For example, if the targeted opponent's life total is 4 when this ability resolves, it will cause that player to gain 6 life; alternately, if the targeted player's life total is 17 when this ability resolves, it will cause that player to lose 7 life. Other cards that interact with life gain or life loss will interact with this effect accordingly.
So yes, it does work.
I'm assuming the art beneath the card reveal is Adriana; she's in heavy armour and I'm pretty sure that's Brago's sword. I'd say an Adriana card is likely based on that art.
Just wait, Odric comes out of nowhere and goes full "Old Man Henderson."
This. The Eldrazi are inspired by Lovecraftian monsters and cosmic horror, but don't really fit into either category cleanly. The reason they don't has more to do with the fact that our POV characters are planeswalkers, who traverse the non-euclidean void between planes as a matter of course. One of the main reasons that inspire the feelings of insignificance in cosmic horror is that the monsters come from far beyond anything that even vaguely resembles our frame of reference. In Magic, our main characters regularly travel through the Blind Eternities, and though the void between worlds is impossible to understand fully, they have some concept of what it is and how the Eldrazi interact with planes. If our POV was a plane-bound being with no concept of planeswalkers, other planes, the Blind Eternities, or any of the things from off-plane that don't follow the rules of the only plane our POV character knows; then the Eldrazi would actually be Lovecraftian cosmic horrors.
So this is how I see this playing out:
Sorin and Nahiri keep trying to kill each other and Liliana keeps poking the Chain Veil, putting Innistrad in greater and greater peril. Tamiyo continues to observe and record, but will probably refuse to get involved. Jace and Arlinn try to stop the chaos, trying to talk sense into the others (Sorin and Nahiri in particular). They will probably fail, Oldwalkers being as unreasonably stubborn as they are, and will be forced to drive off and/or kill at least one of the Oldwalkers, and deal with whatever this looming threat is (be it Emrakul or something else). As for the Oldwalkers, I don't expect them to get directly involved in stopping the "looming threat," as one or more of them is probably causing it, and the others are so fixated on their own particular agenda as to not care. The only Oldwalker that I could see possibly helping is Sorin, but that depends on if he's more concerned with protecting Innistrad or getting revenge at the moment; that could go either way. Whatever other planeswalkers show up in Eldritch Moon will probably fit into these storylines somehow.
TL;DR: Both Sorin and Nahiri are a**hats and are likely to continue being so, leaving it up to Jace and/or Arlinn to actually fix things.
They're separate races in Magic too, though the alignment of the races is different. Demons are usually either lawful evil or neutral evil, but can be chaotic evil. Devils seem to only show up in certain settings, and are pretty much universally chaotic evil. I'm not very familiar with D&D, but I believe that Magic's representation of demons as powerful infernal lords and devils as impish minions is reversed in D&D too.
I think you might be on to something. The plane is creatively inspired by horror tropes, so the kind of trauma that would cause a spark to ignite would likely be more frequent than on a plane like Theros. There, most seem to go their entire lives farming, or fishing, or whatever, and never have a latent spark ignite. Seems much less likely on a plane where gheist/zombie/vampire/werewolf/cultist/devil/demon/yada-yada-yada attacks are so common. Innistrad has to be the worst place in the multiverse to live. I mean, the place does have an actual hell; and one that spills over into the mortal world, no less.
It is kind of contrived that the only four planeswalkers we have trying to save Zendikar are the exact four with the exact skills needed to pull off this insanity (Jace to unravel the solution, Gideon to organise the bait, Nissa to channel the power of the leylines, and Chandra to be the "big gun"), but no more-so than is common in team-up fiction.