Cry for the Devil: Billy. After witnessing both his parents being murdered on the night of Christmas as a child, and being mistreated by the Mother Superior, worsening his psychological issues, you'd almost excuse him for going completely Ax-Crazy.
Ho Yay: When Sister Margaret introduces Billy to Mr. Sims the camera pans up Billy's body, making it look like Mr. Sims is Eating the Eye Candy.
Older Than They Think: Christmas Evil had a plot about a man who had a Christmas-related trauma as a child and who as an adult ends being driven off the deep end, which inspires him to dress as Santa to punish the naughty, four years before Silent Night, Deadly Night (albeit much less controversially).
Ron the Death Eater: Pamela, of all people, with some calling her an Ungrateful Bitch who deserved to be killed, because she didn't thank Billy for killing the guy who was trying to rape her. Even though there's a world of difference between just saving Pamela from her would-be rapist, and garrotting the guy to death with a set of Christmas lights. At most, her actions fall under Too Dumb to Live for yelling at and slapping Billy right after he killed someone, and even that's a huge stretch considering that she's clearly shocked and traumatised.