Antionette
"There are plenty of things that both exist and not exist at the same time. A shadow exists yet doesn't when a light is shined on the same area. I am simply a vestigial portion of another being, nothing more or less." 

She would say and then place a hand on her chest. 

"I could even just be a combined hallucination of you both for being in a graveyard this entire time."
Kirsten
"Ok, Schrodinger's Cat. Enough with the cryptic mysticism and just speak normally. You're not a hallucination cuz I've seen you before and this place is far too dead both literally and figuratively to create something like that. No offense to the ones lost here."
William
"Yeah stop with all the riddles" He then thought of something why was this mysterious figure even here he knows that Xion came through some portal she made he then say "Wait a minute why are you even here Mysterious Person?"