Happy Death Day is a minor slasher remix built around repetition, in a genre already prone to it. Theresa, or ‘Tree’ (Jessica Rothe), is a sorority sister bi-atch who wakes up in a stranger’s dorm bed, hungover and late for class. It’s her birthday, the same as her late mother’s, and she’s in a bad mood, ignoring her Dad’s persistent calls and carrying on with a married professor. She seems to have been in a bad mood for a while. Late that night she gets cornered in a dark underpass on campus by a creep in a buck-toothed baby mask…