So, on a hunch, I took a look back in the main Multiverse page for the backstories of the characters I haven't unlocked yet. They do have all the ones from the newest video game launch up (Gloom Spite, Skinwalker Glomy, Darkwatch Nightmist, ect.)
The reason I started a thread over this is because Darkwatch Nightmist's is very cool and might hold some hints as to her fate later on in the timelines.
So, Nightmist went outside our world (most probably a section of the Realm of Discord) and "reached out into the void and drank deep of the eldritch power she found there" to power-up to fight bigger threats. Then she couldn't return home. She actually became a magical being according to the text and was locked out of our world. She also became a target for other such beings, who she fought for "centuries". Finally she learned of a portal, tossed aside everyone fighting at the mouth of the portal, turned it to point home and showed back up days after her initial disappearance. However, she is still a magical being. This makes it much easier that some mystic force banished her, or perhaps whatever closed the timelines in Tactics might have severed her connection and pushed her back. Also possible that she got super-charged by an oblivion shard and her cursed form/side took over and she's the mist from Tactics (not a new theory, but now with more hows and whys)
Nightmist Tangents:
I wonder if the either the portal or the void from which Nightmist drew power is related to the "Spinning Vortex" in the Realm of Discord, and also if any of that relates back to the The Scholar of the Infinite, perhaps he didn't become a portal as much as line himself up with an existing portal. It is also occuring to me that we have beings called "Portal Fiends" in the Realm of Discord which might reference this. It's possible that the heroes did not previously notice the portal or many of the beings in the Realm because they were not on the correct wavelength being mortal beings as compared to magical beings and Nightmist saw a lot of it after shifting between the two.
Re-reading through Nightmist's backstory I remembered "The Master". I don't remember what we ended up deciding about the Master, but I wonder if it ended up being Zhu Long. Not only is he the only old mystic Chinese guy we've seen, but looking over the arc of Nightmist she seems to the type of person who continually gets involved in bad situations and dark forces that she doesn't understand until it is too late, impulsive to a point since she joins the FV in an investigation before her "Master" thinks she is ready for such tasks. We also do not know Zhu Long's end goal or motivation, so it is possible he played the long game against Nightmist, originally just trying to mold her into a powerful servant for himself but after she went against orders and aligned with the heroes he saw she was gathering power, leading to a completely seperate plan that he launched against her before Tactics. The only "problem" is that we know Nightmist confronted Zhu Long to get Fixer back, but either this was when she recognized him for who he was (doubtful because I think that would have been mentioned) or being a powerful mystic he had hidden himself and she didn't recognize him.
Not sure if this was mentioned before, but GloomSpite and Skinwalker confirm a few things. It seems like Jack Donovan was killed by the Wraith, perhaps secretly or seperate from the rest of the team. Gloomweaver brought Spite back and gave him a mission. Kill a bunch of people and form Gloomweaver a body made from the corpses (I wonder if dismemberment was a signature of Jack's serial killing before this?). If he failed, then his body and soul would be sacrificed and Gloomweaver would use them as his portal into our world. My bet is that Spite failed, because Spite's body was ravaged by the drugs and that made his vessel imperfect, which would explain why Skinwalker's flip side is so self-destructive, the massive power of Gloomweaver could maintain the body for a time, but it began crumbling under the strain and Gloomweaver desperately killed and consumed trying to keep it intact, only to fail yet again.
I also just saw the blog post from two days ago about Villains of the multiverse, some of those are really cool 