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.
They're unhappy about not knowing what's going on and demand fairly extensive explanation of dreamshaping. But they get the urgency. They will have little idea how to rescue Gren and will default to brute force once through the portal - unless this is unwise somehow?
(The technology is, indeed, good news. Perhaps they could get a quick sample of textbooks to throw at some engineers, if it will only take a moment?)
The pocket dimension can contain anything so maybe it will be filled with innocent children or monsters that look like innocent children. The way to solver the trouble is finding the Gren-projection that is in there and bring her through the portal. Felix can't stay dead so it makes sense for him to go instead of risking mortal lives.
Felix retrieves some books he created as a text, it is pretty random engineering, but it looks legit and rather advanced.
Boreal forest, night sky. Rock formations here and there. Standard forest sounds and scents... But with a sort of metallic layer over them.
It would be pretty if he didn't fear of being assaulted by a monster or something.
He takes flight. Any sign of Gren?
The forest turns less boreal and more temperate towards a rocky hill in the center, where a building with huge glass windows shines with too much light.
...Did he see something out of the corner of his eye? A red glint from the forest?
Did he? Well... does it help if he sends some fire balls to illuminate in that direction?
If by 'help' you mean 'elicit a barrage of red beams', then yes!
Also, a near-silent metallic... Cyborg owl? Tries to dive-bomb him, scratching with claws and beak. This one doesn't seem capable of lasers.
The metal owl gets a shallow scratch in, but melts readily. Whatever was below seems to have decided to hide in the thicker trees for now.
Ok, Felix will start gathering electricity so he can be ready to strike. This is his life now, apparently, throwing thunderbolts at giant monsters.
The monsters do not attack again. He's being watched as he approaches the shining house(?), though.
It's like a bizarre blend between a church, a house, a castle, and an office building. Not really matching any of them, with features that try to clash with one another but still manage to produce a coherent and attractive, if odd, whole.
"Could be weirder" Felix says to himself.
Any obvious entrances? Signs of activity?
There's a big balcony on one side with huge glass overlook, might be a door. It looks like some kind of art gallery with lots of mirrors, maybe. There's also a very solid-looking barred door with a path leading down to the forest. There are scorch marks on and in front of it.
It opens fine.
It does look like some kind of art gallery in here. Various objects are strewn around. A flintlock gun, a blanket, a flute, a pantry full of mostly paper-wrapped foods, a wooden cart. A corner of the place is set up like a workshop with 'tools' that don't entirely make sense. The mirrors (and there are lots of mirrors) all reflect a version of things that's distorted in some way. This one reflects things as though they're made of tinted glass, that one makes everything white, this one covers everything in spikes...
There's a big spiral staircase leading down, if he wants to work through the near-maze of reflections and glass.
...Felix will not touch the suspiciously magical mirrors of potential doom. And touching the various objects should be avoided. Can he fly over the near-maze? Or mark the floor by scorching it with controlled fire?
He can mark the floor just fine. There are more mirrors on the ceiling, and there might be a clear path, but the light's playing tricks here and it's hard to be sure.
The sound of breaking glass comes from below, and a growl of frustration.
Urgh. Felix thinks. Call out and attract attention? Gren can't die in the dream, but not waking up could kill her...
Felix swallows and yells "Gren!?"
"What now?! Nightmare can't kill me with animal-Neuroi so, what, it's trying psychological warfare?"
"What? No. I'm here to rescue you. We need to talk you through a portal or you won't wake up."
"Yeah, sure, I believe you." She doesn't. More breaking glass. "I don't even know you."