ETA: There is now a third thread, so send new comments there.
Since the first thread has exceeded 500 comments, it seems time for a new one, with Eliezer's just-posted Chapter 33 & 34 to kick things off.
From previous post:
Spoiler Warning: this thread contains unrot13'd spoilers for Harry Potter and the Methods of Rationality up to the current chapter and for the original Harry Potter series. Please continue to use rot13 for spoilers to other works of fiction, or if you have insider knowledge of future chapters of Harry Potter and the Methods of Rationality.
A suggestion: mention at the top of your comment which chapter you're commenting on, or what chapter you're up to, so that people can understand the context of your comment even after more chapters have been posted. This can also help people avoid reading spoilers for a new chapter before they realize that there is a new chapter.
What immediately occurred to me (similar to the infamous scene in The Princess Bride), is that if your opponent believes you will have a distraction and a real attack, simply lauch two real attacks, with the expectation that whichever one the opponent takes to be the distraction will succeed. Obviously this requires a greater sacrifice of materiel, but Quirrelmort doesn't exactly seem short in that department.
Do one better. Have an obvious distraction, a less obvious distraction, and one real attack. That way, when your adversary discovers the less obvious distraction, he'll stop looking.