I was under the impression the unicorn was Alicorn's cameo. Alicorn asked for a cameo as a unicorn, Eliezer agreed and even promised to make it plot relevant. I'm not sure what actually happened was quite what Alicorn had in mind.
There were two, one was Alicorn and the other was Twilight Sparkle (unnamed).
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 102.
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: