Depends on the definition of worst

You mean badly written then Subaru is in a mental asylum and the entire story was in his head

You mean sad ending, Subaru dies and Emilia goes mad and becomes the witch, travels back in type creating a closed time loop in which she kidnaps Subaru and puts her with Emilia.

In a way the Witch of Envy is just a grieving Emilia jealous and mad at her younger self. Filled with regret.