Terrifier 2 hints at a major connection between Sienna's dad and Art the Clown, suggesting that he may be the reason Art is terrorizing Sienna and her community. Sienna's dad owned a magical sword that plays a crucial role in the movie, raising questions about his connection to Art and their potential link.
While you don't necessarily need to see any of the previous films to enjoy all the mayhem, if you want to be a completist, watch the Terrifier franchise in the following order.