To give credit to the eldritch sigil theory, it turns out that the new people in his room have bat-like wings and horns...

...and tails with an arrow-shaped tip at the end. Which Morty might not notice because once he can see the tails he can see how very naked they are.

The only thing they have on their person is a book. The smaller one uses it to cover himself.

Morty covers his eyes. "Gross! Why are you in my room! And naked!"

The two naked demonic looking boys exchange words.

Then one says. "Comprehend Languages." then he points at the other boy. "Share Languages."

The words sound like every language Morty understands, overlapped, but comprehensible. "What just happened?"

Conveniently, Morty only speaks English.

"I don't know! I was stimming with some cardboard and then it blew up and then you guys were here! Are you guys- demons or something, or do you just have GSD and teleporting powers?"

"The translation is undecided on the word 'demon'. We don't have any form of teleportation. What's GSD?"

"Did you do this to us? Not cool, first free time we had in forever."

"GSD, it's what gives people - wings and horns and stuff, or turns them into slime monsters, or whatever. I think you guys are demons, this is above my paygrade."

He goes for the phone and punches in a code. "Miss Hartford, I think I have demons in my room. -oh. Okay, but two naked guys with horns and wings suddenly appeared and it's really weird. No! No, I had nothing to do with this, I swear to God. Can you just- oh. Okay."

He puts the phone down and looks at the possibly-demons, then looks away again. "Okay. Hartford's sending somebody."

"Great, who is that?" One of the possibly-demons says sitting on the bed and using a wing to barely cover himself.

The other possible-demon does the same and looks around. "Is this Prime?"

"Dunno what 'Prime' is. Ms. Hartford is the administrator of the school. -this is a school, by the way. She sent somebody to assess whether you're dangerous or not."

"Prime is the name for the human world. Are you human, right? Are we in trouble?"

"I'm human. I don't think you're in trouble, but you're here, and that's weird and kind of alarming. The school's priority is gonna be getting you back where you came from. Unless you don't want to go back, and you're not evil and dangerous, in which case you might be able to stay. It just occurred to me that maybe Hell isn't super great and people don't necessarily want to be living there."

Frown. "The translation is weirding out on the word 'Hell' too, our word for our world is 'Tartarus'. But we don't necessarily want to go back."

"Military life is really not for us. I like the access to hot guys, but everything else sucks." He winks. "I am Gavriel, by the way."

"If you're looking for hot guys, Whateley's the place for it. I mean, if you're a teenager. It is a high school. But like, a really weirdly sexy high school. Aaaand I'm Morty. And I'm straight, sorry."

"Aw, too bad. But your heterosexuality is forgiven. Herod, can we stay in the sexy high school? We are teenagers, right?"

"I don't remember the difference between Prime and Tartarus' years, but I think we are. And what do you mean with weirdly sexy?"

"Most mutants are Exemplars, which means they look older than they are and tend towards being conventionally attractive. They also act older than they are. This extends to having a bunch of sex all the time. The school does approximately nothing to discourage this."

There's a knock at the door. Morty opens it a crack. "Hello?"

The door swings open the rest of the way, revealing a young woman dressed in chainmail with a battle hammer at her belt. "Hello!" she says. "Oh, cool, naked people! What's up with that?"

"Hi! We just showed up here all the suddenly. And while this one didn't admit to anything, I think it was his fault, somehow? Anyway, hi! I am Gavriel and Herod forgot to introduce himself properly."

"Hi..." Herod says covering himself and blushing. "You are the one who was sent to talk to us?"

"Morty, did you fuck something up?"

"No! I was just playing around with some cardboard and it turned into some kind of eldritch sigil and then there were naked men in my room!"