Happy Death Day 3's proposed storyline has been revealed by the franchise's writer-director Christopher Landon. The original Happy Death Day combined the premise of Groundhog Day with a traditional slasher, turning a victim, Tree Gelbman (Jessica Rothe), into a final girl by putting her into a time loop that resets every time she is killed by a murderer in a baby mask. That film was a hit, garnering the 2019 sequel Happy Death Day 2U, which found a more sci-fi-based premise as Tree found herself forced to continue resetting the loop in an alternate universe in order to get back home.

https://screenrant.com/happy-death-day-3-story-details-cancelled/