Half-Blood Prince

I finished Harry Potter and the Half-Blood Prince and enjoyed it a great deal, probably the most of all the books in the series so far. (Yes, I've been having a good run of books and movies lately. I do dislike things sometimes, honest!)

The statute of limitations on this volume probably passed a while ago but just the same, let's hide my spoilers under a cut. ( So what would happen if, like, Dobby fired an Avada Kedavra at, like, Galactus? )