His stores of Allomantic metals abruptly disappear. They're still physically there, but the power is completely gone. He immediately turns to go back, only to see more forest.
At least his Feruchemy still works—he can tell because he's still alive—but that won't last him forever. He only has so much stored youth, and without both sets of abilities he can't replenish it. He hasn't been in so much danger since the beheading that one time. Returning to Scadrial is the highest and currently only priority. If spontaneous forests are a thing, he needs to find someone who can explain them and more importantly how to get back.
The next few hours are spent walking in an essentially randomly chosen direction, with the sun to his right. He's quite certain that suns are supposed to be moving across the sky, but that's not a pressing emergency. He already knew he wasn't on his own planet when he saw proper trees and plants instead of ash-covered monstrosities. Whenever he calls out, nobody responds. If it's an empty spontaneous forest, he's probably doomed.
After some time, he hears his stomach growl. He hasn't seen much that looks edible, but possibly that's just because he's not used to real plants. Berries. Berries used to exist. Those berries look tasty, and if they're poisonous it's not like he needs to worry about it. As always, he has a truly ridiculous amount of stored health in his gold jewelry. Tapping gold just in case, he eats a handful.
He's not getting out. Especially once the removable objects are gone. The bracers on his upper arms don't get removed, possibly because they're thoroughly attached to his arms via spikes, but he's left with no metalminds except the ones keeping him young. And, of course, a piece of gold he had implanted in his jaw after the incident with the beheading. This adds up to: No metallic means of escape.
They continue patting and prodding him. They inspect the bracers, then leave them alone. They wait for another minute of dark dark dark, noise noise noise. After this minute, something sugary is insinuated through the chain gag in his mouth. With a long utensil to push it down his throat. Yummy. This happens three times.
It sucks to be him even more, now that he's tinless and the noise is back. That's probably not his biggest problem right now.
He reverts to his chronological age, and also starts to not breathe. These do not combine well for him.
"Not yet," says another woman's. "Keep him alive, without loosening his binding." (Air feeds itself into his lungs without his intervention. His aging reverts, although not much.) "Throw him in the dungeon." (Someone picks him up and begins to carry him away.) "See to repairs. Determine who he subverted on his way in. Renew their orders. Put out his eyes." (Someone puts out Alendi's eyes. This is a standard amount of painful.) "Call in Flay and Whetstone. Restore the light." (Alendi has no eyes and may not be able to appreciate this.)
Those are not names of people Alendi wants to meet. He resists with every action he conceivably can, which is none.
Alendi, eyeless and kept breathing and not shriveling to death solely on the sufferance of another's sorcery, is carried out of the room, tossed casually down an empty fairy "stairwell" and allowed to hit bottom in a way that only breaks his hip and both legs and not his skull, and then picked up again and carried some more.
The dungeons are (as far as the blinded prisoner can tell by listening and feeling) earthen pits, with grates overhead. He is dropped into one. Ow. The grate is shut with a clang. There are footsteps, retreating; more approach and fade, as though there are patrolling guards above his pit.
He lies where he lands, and stays there until further notice.
This can't possibly be Yellow's initiative.
"Mmph?"
Chain. Of course.
And one of the links on the chain breaks. The entire thing is a continuous mass; he could wriggle out of it now.
"They came up with something I couldn't break. Magic stone of some kind.
But I got off a dart first, and if that can get past whatever defenses we don't know about then it did."
"So you might have got her? You got close enough? You don't have your name - did she feed you, did she order you?"
"Three people fed me. She might have been one of them—I certainly would have, in her position—but she didn't order me, so I can't say for sure whether I got her."
If it were definitely a good idea to try anyway, I'd need my metalminds. Those got captured, but I can make more. Can you make a gate big enough for me to come through?"
"The harmonics in the pit are terrible and we're running out of time. And the dungeon has guards; you'll be noticed if you go out of the pit unless you can incapacitate them as-is or with something I can pass through this little one."
And it is definitely worth telling them about Compounding for this."
"Give me the list; I don't think I forgot any but just in - shh," she says, as footsteps approach.
"Iron, steel, at least five pieces of tin, pewter, zinc, brass, bronze, chromium, atium. Cadmium and copper too, I suppose. I've already got gold.
Also the spikes that give Feruchemical zinc, steel, iron, and pewter so that those metals can come already charged. Make sure to tell the people the spikes come from about burning metalminds if they haven't figured it out already."