"Hold on," Jessica starts to say to him, though it only comes out as a neigh from your uncle's perspective.
"'What's wrong?" you ask her mentally.
"Well, this feels real, John. It doesn't feel like a costume. Especially after...well...that," she nods her head to the unicorn foal.
Uncle Jack stops, noticing you neighing to yourself, and waits, petting the little foal.
"Okay, I'll definitely give you that. But maybe, I don't know, it's still a costume for others, and they can take it off? It's worth a shot. What's the worst that can happen?"
"Oh, you just had to say that," Jessica groaned.
She smiles involuntarily. "I didn't say that, you did. Hehehe."
"Har har, at least I'm not the butt," she mentally replies.
While you two banter, your foal seems to have started crying, and his or her (you still haven't checked yet) horn seems to be glowing. The foal has the horn aimed at Uncle Jack.
"Woah there, calm down little one. I'm just going to try to bring your mom and dad back to normal. Hopefully you too after," Uncle Jack says, trying to assure the foal. But it only makes the foal more nervous and scared as he walks over to you and Jessica, the scary unfamiliar man approaching the foal's mama.
"Watch out!" Jessica calls out, but the loud neigh isn't enough, as the foal sends a blast of magic at Uncle Jack, sending him to the floor in pain and spasms.