I remember in one of your posts you said the concept of mastermind nagito casing sdr2 for makoto would be fun and i kinda want to know more about the idea. How it would go, how would he use junko ai (like izuru just put it in and went into a pod). Would he find a way to do more, like making sure there was a possibility that makoto could come in at any time without being ousted, would it be like a test of hope to see how strong makoto's hope is (it's def that) or does he wants him to defeat enoshima again and wants to be there to see it, bonus points if he's flirting/ fangirl over him if he retains his memories (like he would somehow find a way to make sure he remembers from the get go or he gets to the final dead room and remembers and is suddenly looking at the sky weirdly at night and talking to makoto when they get out and it creeps him out) or during the final trail if it's the same as last time where he can't get in to save them.
(To answer your actual question, yes, he plugs in Junko's AI like Izuru did. Probably some amount of conversation happened between him and Alter Junko while he was in Towa City, and they probably both would love for her to leave the door open for Makoto, but I'll put a pin in that for later.)
Oh boy, what I most like to imagine is Mastermind Nagito being in the simulation with all his outside memories and having the overall attitude of someone directing a children's play knowing someone important will be in the audience.
Like, he starts out with a generally positive attitude. He's decided that Hajime is the protagonist, for projection reasons, and obviously Monokuma is the antagonist. Any early complication is just a vehicle for character development later, so he's not terribly obtrusive.
But then as the killing game goes on, he starts getting regularly annoyed with everyone involved, often to the point of leaning on the fourth wall.
An uninteresting group conversation drags on too long? "I feel like we covered Fuyuhiko's trust issues already," Nagito says, with a passive aggressive smile. "Why don't we give someone else time to talk?"
Monokuma's third motive is "despair disease"? (And presumably Mastermind Nagito doesn't contract it.) "Literally changing your participants' personalities?" Nagito says, rubbing his head in annoyance. "I don't think any audience would find that compelling."
(Monomi he treats like a noisy theater attendee; he's always shushing her or waving her away. This works on her for some reason.)
Hajime trying to wait out the Funhouse motive? Nagito literally pulls him aside like, "Don't you think it'd be kind of embarrassing if our so-called protagonist didn't do something daring every now and then?"
"I never said I was a protagonist," Hajime protests.
"No, I did," Nagito says. "So don't embarrass me. Or if you must, at least kill me."
The other side of this is, eventually he kind of internally goes, Of course. There's only one Ultimate Hope. It was a waste of time to try to build a new protagonist. Didn't Komaru Naegi prove that already?
And he gets abruptly mellow with everyone. It's back to his earlier positive vibes. No one's disappointing him, and he apologizes for being weird.
And he traps everyone in a situation and basically holds them hostage to lure Makoto into the simulation.
Something like, Nagito drugs all the food, and while everyone in the dining hall is still eating, he's apologizing specifically to Hajime.
"...And I'm sorry," he says. "For that 'protagonist' stuff I said earlier. It was unrealistic of me. Of course, you weren't the one who embarrassed me. As always, I embarrassed myself."
"Dude, I said it's fine," Hajime says uncomfortably.
Nagito smiles warmly. "That's something I really appreciate about you, Hajime. It's why I thought you could be...like him. But you were like me, and deep down, I think I knew that from the start."
"What are you...?" Hajime's words are slurring, and the drugs are seriously starting to take effect. "What...?"
"You stay there. I'll be right back. Akane's trying to take the stairs, and we don't want that."
Once everyone passes out, Nagito is making blatant eye contact with the cameras and talking to Makoto directly. While, idk, soaking the whole room in gasoline.