That's assuming that the stone is hidden somewhere and the mirror merely allows information on its location. In canon, (or, at least, going by my memory of the movie) after HP saw himself in the mirror finding the stone, it materialized in his pocket.
Why the assumption that the trials in HPMoR are going to be even remotely similar to canon? All we know at this point is that the Mirror of Erised plays a part, but we don't know what that part is, or what any of the other trials are, etc. Using canon information to make deductions about HPMoR has proven a less-than-reliable method in the past, and EY's essay on originality suggests to me that the obstacles will in fact be radically different from those in canon.
New chapter!
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 104.
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: