The 13 days of Christmas have been made special again by daily gifts of stories or art allowing intimate insight in the lives of the Hogwart's staff. To pick just three to point out especially is difficult, but one can try:
1) Severus Snape kept a very special diary as a student and then again as Headmaster; it is a Prince family heirloom protected by very unique magic which decides who may have access to its contents:
https://hoggywartyxmas.livejournal.com/89240.html (PG13) 1.Bitter, 2.Sweet
2) Hilariously funny is what happens after the ghosts of Hogwarts soak in vapor of Amortentia and decide to spread the good cheer:
https://hoggywartyxmas.livejournal.com/93383.html (G) Ding Dong Merrily On High
3) A whole branch of magic not covered before opens in Bibliomancy which tells about Irma Prince, her magic, her life, work, friendships and loves:
https://hoggywartyxmas.livejournal.com/90768.html (PG)