Anywhere in the story, possibly as a result of a situation originating from Forge tinkering:
If we can confirm its existence, then it interacts with the physical world. If it interacts with the physical world, we can, theoretically, blow it up.
“Sara Louise Adrien, what a surprise seeing you here,” said the Doctor. He’d just literally run into her as the worlds changed.
“Ah,” said Sara. “You again.”
“Still dimension-hopping?”
“Yes, although, this time, I somehow managed a double hop. Not my fault. Sergeant Slash, over there, thought the integrator was a bomb.”
“My name,” said the body armor with a face in its depths, “Is Captain Carnage.”
Sara rolled her eyes. “Everything we imagine is a reality I can fade into. She’s from a video game.”
“And I’m television. You tell me last month.”
“Ugh. Nice to know it *still* won’t be solved.”
“Wait,” said Captain Carnage. “What?”
“Temporal mechanics,” said the Doctor and Sara together. Sara added, “Don’t think about it too hard, dear, you might lose some hearts.”
“Yes. Well. Glad to know we’re all acquainted. Can we get back to running, now. We have a slight problem with an ectoplasmic temporal echo.”
“What?” said Captain Carnage.
“Technically speaking, and dumbed down to the lowest denominator,” said Sara, “a ghost.”
“And this one’s very cross with me about something I haven’t done yet.” The Doctor glanced behind him and broke into a run.
Sara started jogging next to him and Captain Carnage lagged behind. Looking behind her every three steps. “Well, the good news is, you have plenty of time to go and fix it. Unless it’s a fixed point, in which case, it’s very bad news indeed.”
“But what can it do?” said the Captain. “It’s a ghost.”
“Well… currently, it’s throwing things. Sharp things, mostly.”
“If we can confirm its existence, then it interacts with the physical world. If it interacts with the physical world, we can, theoretically, blow it up.”
“Very nice logic, dear,” said Sara. “The only problem with that is that blowing things up isn’t the go-to solution in this universe.”
“That’s not a lot of fun,” complained Carnage. “I should rescue you. You’re clearly NPC’s.”
“No! You’re in a cut-scene! This man has been in this universe for well over nine hundred years, faced down every kind of Boss and did it all with a screwdriver,” Sara desperately babbled. “And he did it all on two hearts!”
“Two?” repeated Carnage.
“Just two,” said the Doctor.
“So… he’s like a technomage.”
“A lot like a technomage. Do try to keep up! Physically, too!”
[Muse food remaining: 5. Submit a prompt! Ask a question!]