Man, you guys are terrible at this guessing game.
I mean, the Cornish pasty is one of the smallest Tyranid breeds, it clearly wouldn't come in an egg that size, even if there were two of them.
So, what is Lilith the wishing mirror spirit from?
Also for BD, will the metroid get to be a recurring character?
Er, Rosario + Vampire. That was the mirror that was stolen from the campus and given to Tsukune's cousin so that it could wreak havoc during the festival. So I felt it was an obvious item to include in the Headmaster's stash.
Did I throw you guys a curveball by actually referencing canon for once?
As for the Metroid, it's a secret
I can see it now. Canon Tsukune joins in on the 'What kind of monster is Ranma?' bandwagon, and gives the only remotely correct answer: spider god.
And then he gets laughed off by all the characters that know better, because what would a GOD be doing going to high school at YA? Ha! That's so silly!