They both contain people who communicate with people from the past. They also try to save people who they love with this method.

They are both about a single parent who seeks revenge on their daughter's rapists. I find broken better than don't cry mommy. But they are both good movies.

They have similiar plots. In Happy Ending the father has cancer and prepares to say goodbye to his family. In Mama the mother is terminally ill and prepares to say goodby to her son. (and find a family for his son)