There in fact is! It is the Bloody Baron, dripping ectoplasmic blood here and there.

"Excuse me," he says, to the bloody ghost. 

"Hello, young man," says the Baron in his hollow ghost voice.

"How are you? Did you have a good summer?"

"Why, yes, thanks for asking, how about yourself?"

"It was nice," he lies.

"I'm Scott. I'm a first year, this is my friend Sadde." 

"My pleasure to meet you both, and be welcome to the great Slytherin House!"

"Hi! So are you really really dead?"

"Well, yes, that would be the thing that happens after you stop being alive."

"Do you ever get lonely?"

"Hmmm, can't say I do, no. Even when the students are out, this castle is quite lively."

"Do you have any friends?" 

"Hmm, a few, yes. Do you?"

"There's Sadde! And...hi, I should have said hi, that's not very polite." 

He directs that last at Nyle.

He half-smiles. "Hi, indeed."

"Well, that's good. You will need your friends to achieve your goals; cherish them. Now I must be going!"

He lets out a ghostly moan and moves on.

"That was cool. I've never met a ghost."

"You get used to them," Nyle shrugs, apparently having decided to studiously ignore Sadde's existence.

"I thought they would be more like paintings."

"What do you mean?"

"I don't know, he seemed less excited than paintings are? Paintings are always telling you about the person they were."

"Hmm, I dunno, maybe he just didn't want to talk about himself."

"Ghosts don't tend to get too fixated on their life," he says, still ignoring Sadde.

"Maybe he didn't want to talk about himself. Is he very private?" 

"...somewhat."