"Let me just--" 

She glows. Her light acts like sunlight in throwing rainbows off of Addy's skin. Her light acts unlike sunlight in that it immediately regenerates any burn damage Addy took before she put herself out. And any other damage she's taken over the centuries; scars from other vampires' teeth melt away. 

"Oh, wow, that's a very cool ability. How's it work?"

"I imagine that if I say I'm the daughter of the Mountain of Light this will be less elucidating for you than it would be back home."

"Little bit, yeah."

"What if I say, 'I am one-quarter star.'"

"...I continue to have questions!"

"I am only half-human. There have been no instances of humans having sex with full-blown stars. My grandmother was much smaller than a star and much larger than a human."

"Cool. That is aesthetically concordant with the fire." She turns to the floating one. "How about you, your handshakes hazardous?" She sticks her hand out.

(She says her handshakes have never done that before. I am not going to shake your hand until I know why you caught fire, even if you've solved why you caught fire.)

"I'm very flammable."

(...Okay.)

She tentatively extends one hand. 

Instead of four fingers opposing one thumb, she has three wide digits each positioned equidistant from the others. 

Addy will gamely try to figure out how to shake this hand anyway.

On Mewtwo's end, it mostly involves grasping Addy's fingers with her mutually-opposable digits. 

It is a disappointing handshake but Addy doesn't complain. "Charmed!"

"Sorry for setting you on fire, that really doesn't usually happen. I wasn't even--I mean, my light doesn't set things on fire; my language does, sometimes, but I don't set things on fire with it by accident...I'm pretty sure it's some kind of magic system interaction but I'm curious what the magic is on your end. Besides, uh, whatever makes you flammable."

"Well, I'm a vampire."

"--Okay, that doesn't give me a good working model of how it interacting with my everything set you on fire but more importantly, do not drink my blood. Do not. It is a bad idea. I say this not because I expect to suffer the usual consequences of having one's blood consumed but because historical precedent suggests you will regret it even if it doesn't set you on fire."

"Noted. Cafeteria's got me covered."

"Good. It's not, you understand, that I specifically suspected you of it, just, it's very dangerous. And the way in which it is dangerous would not involve you dying and getting neatly picked up by the Death Ward."

"Oh really?"

"My light is incredibly vitality-promoting. Someone shoved a chunk of my father's flesh into a guy once and now the guy is an island, every inanimate object from which is alive. The ones that are sentient and the ones that are independently motile have areas of non-overlap. Nobody involved is happy."

"Well that sounds fascinating but I will not snack on you unless I come over determined to explore islandhood."

"The King With a Thousand Hearts did not actually eat the flesh of a sentient being, and, probably not coincidentally, is the single most harmless relevant example I could think of. --Sorry, I'm--I can't say 'taking this too seriously' but perhaps being too serious at you in particular."

"You don't need to worry about me. I'm in full control of my diet."

"And things are different here." She shakes herself and goes off to acquire food, her roommate darting along behind.