One who uses this will be cursed—or blessed—with Noxophilic Sanguivoria, and will become a Child of the Night. In other words: a vampire! (Priests of Arkay can cure this affliction, if desired.)
Crown Store items are purchased in the in-game Crown Store. To buy any of the Crown Store's special items, you'll need crowns, a virtual in-game currency. Crowns can be purchased in packs of various sizes, and you'll receive a discount on larger packs!
You can get a monthly allotment of Crowns by signing up for an ESO Plus membership! Learn more about member benefits.