Both are young adult novels that my best friend read as a teenager.
One is about an ancient Egyptian called into the present by a spell or something. Romance novel. The girl who called him into the present had an amulet with blood in it, that she found in an antique shop.
The other book was a werewolf book in which there’s a scene in which a good werewolf grabs a silver cross to defend herself, using it against a bad werewolf, and the cross hurts her as much as it does her enemy.
Not much to go on, I know.