They are in a mostly-empty room, except for two chairs and a mirror that's probably a one-way window.

"Hello. We'll bring them one at a time and see if they can affect you, is that alright?"

Meeting with strangers and masters to check if they affect me.

"Yeah."

Oh. Good luck.

Legend nods and flies away, through a door.

Thanks.

A few minutes later a cape walks in. They're wearing a pierrot outfit, very fancy and clearly made of incredibly expensive materials. They incline their head and take a seat opposite Fëanáro.

"Hi."

The pierrot looks into Fëanáro's eyes and raises one hand.

He raises the corresponding hand.

...huh. He tries to teleport away. 

That works fine. He teleports back - "want to check if I can make stuff -"

The pierrot nods.

Fëanáro nods along.

And he tries making a sandwich.

A sandwich is made. The pierrot (and Fëanáro) tilt(s) their head(s).

Okay. That's everything to test - I guess except whether it keeps working if I've teleported away...

I cannot hold you if I do not know where you are.

The pierrot inclines their head again, waves, and breaks the connection.

"Weird. Thanks."

The pierrot stands up, bows, and leaves.

Okay. Are there ones who might be able to use my powers or make me do it...

Yes. We're sending one in.

Someone wearing a completely white suit with a mask covering the top of their face and head with a swirly black-on-white pattern to it walks in. "Good afternoon," she says.

"Hi! Thanks for experimenting with me."

"My pleasure." She sits. "Now, this is rather unnerving for other people, I'm told."

"Yeah, Boots'd find everything about your world super super terrifying. It's okay."

"If you'd please look into my eyes?"

He does that.

"Now please keep looking into them and try to ignore what my hands are doing."

She starts moving her hands in strange ways.

He wiggles but keeps looking at her.