(Ignore how I thought I'd reply to this after the semester was over and then completely forgot)

Another passenger is on board. They feel like they belong here, with an elegant air about them. Pure white hair, a top hat, and even a deck of cards laid out on the table--they certainly seem like a distinguished passenger.
That being said, they have a totally disinterested expression and demeanor about them. They react to neither the broadcast message nor the newly boarded passengers. 
...truly a questionable choice to socialize with. 

Although there is little to no indication that they are the one being talked to, they seem to know the fact intuitively somehow.
Now, how they show it is a different matter. They don't smile, or turn toward the pair in any way. 
He simply makes some kind of beckoning gesture toward himself, and then keeps his hand there. 
They're probably making sure they're the one being talked to, or something like that.

Having received confirmation, they turn around so that their face is visible.
It appears they are younger than they seemed. Then again, a teenager decked out fully in formal clothing will probably do that. 
They bring their hand closer to their forehead, and then close the fingers between their thumb and pinkie--
'Why?' 
Well, they do say not to eat or drink things from strangers, even if you're on a...strange train, one would suppose.

An introvert would probably be a lot less relaxed after this interaction, but fortunately, the stranger is just a weirdo. The logic given to them seemingly checking out, they simply nod and rear to their full height.

They are. Very tall. 

But anyway, they hold out their other hand, which is now conveniently holding the teacup that Echo offered earlier. Or maybe it's just an identical one? If Echo looks back at his hand, it seems the cup is indeed gone, but the weight is still there.

They sign some variation of thanks, though it doesn't seem as conventional a signing as before. Their body language makes it apparent. And by that, that means that they have placed a hand onto their heart and executed a full bow. While holding the teacup and not tipping it over.
That part's probably to say "Nice to meet you" back.

Uhh, they're signing "death" toward Echo.  

They give an (assumably appreciative) nod, though they don't appreciate it enough to continue standing up. They take a seat again and sign, 'Work.'
Didn't seem like they were doing much work. 

'Interesting. Favorite book?' Simultaneously, with their other hand, they point to themselves and sign, 'Magician.' 

'Thank you' is addressed toward Echo, and then 'Dungeons?' is addressed toward Arete.
It doesn't seem like Death likes talking too much. Or do they like it? They really give off mixed cues.

That was not what they were asking for, but of course, that's the price you pay with single-word replies. Aware of the fact, he simply goes along with it. 
'Dog eat dog,' he signs, which probably means he understands. Either that, or it's a suggestion of some sort. 

Death tilts their head. 'Dragons in dungeons?'
Almost like...Dungeons and D...(the narrator is dragged away for moral reform.)

They consider her response for a moment, following up with: 'Komodo dragons?'

'Shame.' They nod, and finally drink from their tea.
...why is their tea so red?

They shake their head. 
Looks like they don't consider any of those as fitting the definition of a magician. 

They seem either amused or bemused. Or maybe both.
'Are you?' they merely ask in kind.

They smile back, like a ray of moonlight through a patch of clouds.
'Fancy right now?' they ask.