It came out of nowhere.
Felix was flying through the shattered skies, enjoying the sights of the many portals, taking the occasional selfie. Then the threads of energy formed between the portals. Felix almost flew straight into one. That kind of thing never happened. And the threads multiplied and filled the air until one...
...Felix now is somewhere else entirely no idea how he got here. While flying through the wilderness the pain starts and eventually culminates with a blood-covered pebble coming out of his mouth. Which was only supposed to happen if Felix was somewhere else so far that the magic that allows his immortality couldn't reach and the only possible place like this would be another universe entirely.
An hour, he gives himself that much time and uses it, but by then Felix decides that crying isn't useful anymore no matter how much he wants to.
Instead Felix searches for civilization, since he is going to stay in this world for the foreseeable future.
"Oh, that makes way more sense. Anyway, once we go through the portal it should be safe. What else we might find along the way?"
"This place is giving me things that sneak up on you and stalk you... Let's fly nice and high, that should help."
"Okay, just go down if things start to get grayish. It means you hit the edge of the dimension. The horizon beyond that is illusion."
"I'm from another world, no idea how I got here, met some of other witches while fighting a Neuroi and they took me to your base. I recognized the situation when you didn't wake up and came here to rescue you. I'm immortal too, so it is safer than risking someone life."
"You're immortal, can I get that? Really don't want to keep having close calls with the Neuroi. They seem to have it out for me in particular, sometimes."
"Sure?" Felix says uncertain, "I mean we should get out of here and wait until some peace and quiet first. My immortality works by having a floating bolder with a fountain where I emerge from after a week of losing my body, so it is inconvenient to lose a body," beat, "but less inconvenient them death, obviously."
"Quite."
She seems to see the owl-thing that swoops down on them well before it should have been possible, and blasts it with the same lightning bolt that Sparky produced earlier. "Gah. It appeared from nowhere, tracking power says so. Smoke to monster. Stay alert."
Felix remembers to gather lighting. He also prepares to attack with fire.
"Argh. I hate new dimensions. You can't know what is going to jump at you."
"Is this supposed to be the physical embodiment of my mind? Because it got the lingering paranoia-watch-for-threats-on-every-corner right."
"Kinda, as far we can tell. We are not sure how accurate it is, recurring dreams seen to influence it somehow."
The portal shouldn't be very far ahead and Felix will open as soon they are close enough.
There's a pack of Neuroi-wolves waiting for them. Gren bombards them with lightning before presenting a shield and charging right the hell through, toward the portal.
...And when Gren's goes through the portal she "vanishes" only to wake up in the infirmary, safe and sound.
Felix also tries to charge through, using wind and fire to keep the neuroiwolves away.
These monsters are not that strong. He might have had trouble if he set out to destroy them, but getting past is easy enough.
Aaaand as soon he is past them, Felix closes the portal and goes through the other portal to report what happened.
"Gren should be already awake..." Felix then explains what happened inside Gren's pocket dimension.
"...Yeah, she's moving again. Today's gonna be a good day after all, maybe. Are they all that strange? The dimensions."
"They can vary greatly and be quite arbitrary, one is a vast empty space filled with floating platonic-shaped crystals, plenty have monsters or various ambient effects that can be dangerous."
"Well. We appreciate helping deal with the magic thing that you either brought with you somehow or followed you."
"It was no problem. Now that was cleared up, we can continue and discuss how I can help you against the Neuroi?"
"I am not an engineer. My engineers are very excited about what you made earlier but I can't understand a word of it. I've already sent telegrams to several important people insisting that this is not a joke and luckily they take me seriously enough that they're sending a major and his staff from the Unusual Resources Division."
"Oh, good. Not sure how obvious the applications of dreamshaping are. But just a few ideas, they are excellent shelters. And they coexist with regular space but bypass obstacles, so I can create train networks or go through the Neuroi defenses. I can only expand the dimension, but I can create or destroy portal as needed. Also, some of my technology is very destructive, but... Well, I want to know more about the Neuroi first. Are they aliens or something?"
"The Neuroi don't have defenses as such. They just make it untenable to maintain human presence, wherever they move to. Train networks are still useful. Are you implying there could or will be more of these dimensions? Neuroi are probably aliens, as far as we can tell. Nobody saw them arrive, but they don't register as magic, all attempts to communicate with them or discern their language have failed, it's like they don't even have one. They turned Ostmark to ash and moved on to the rest of the world soon after."
"Maybe? I don't know how that piece of the dreamshard got in here."
"If they are not magic at all. I might be able to duplicate the Neuroi technology."