Can anyone tell me what you get for returning his die? Is it JUST the achievement, or is it the achievement along with other things? I haven't seen it talked about on here or in the EPICon section either.

You also receive a book called The Ultimate Guide to Mazes and Mahars - 9th Edition

Aha, thank you! I thought there was some sort of item prize but I just couldn't find any threads about it :)