So here's a fun game I play in The Leaky Cauldron.
Sadly, I have to disappoint you by confessing that this is not my invention.

You have to guess what the other person is.
When you guess correctly, it will be up to you to come up with a clever riddle for another person to guess.

Here's an example:

First person:
I'm only seen by people that have seen death. I was in a Care of Magical Creatures class, and it is rumored that a hair from my tail is in the Elder wand. Who am I?

Next person:
You're a Thestral :O

I came from a land in Europe only to be thrust and stunned in a cage and chained while I protected my eggs from a boy on a broomstick. I am most famous for my dangerously armed tail.

Yet another person(anyone):

Are you the Hungarian Horntail?

I guarded the portrait entrance to the common room when our dear lady couldn't. Making up ridiculous passwords everyday is my specialty. Poor Neville...:)

And so on.
Remember, you can have as many goes as you want at asking/answering
Have fun with it!
Here we go...