My Arbitrary Day Santa did an amazing job. Through their use of dark magic and wizardry they not only discovered the exact series I was currently reading (Mistborn Trilogy by Brandon Sanderson) but they accurately picked the day I would finish the third novel and promptly had the fourth book delivered that day. Its an autographed copy also.

I can only deduce that my secret santa found my city of residence through social media and online stalkery. Due to the the fact that I have a large dog they may have correctly assumed that I lived outside of the city and commuted by train in. This is most likely wear they found me. Through clever social engineering tactics and shear patience they saw where I was in the Mistborn Trilogy. Over days, perhaps weeks of close observation they were able to accurately predict the completion of the third Mistborn book and have the fourth delivered on THAT DAY!

Well done sir/ma'am, well done. As I do not possess this skill of wizardry, I haven't been able to find their Username.