Avengers: Age of Ultron introduced a new level of darkness to the Marvel Cinematic Universe, and this fresh tone was only heightened by the inclusion of nightmare sequences induced by Wanda Maximoff. Earth's Mightiest Heroes suddenly had their worst fears realized in front of them, and to make things worse, they couldn't escape. Each one brought them closer to tearing the Avengers apart.
Source：https://www.cbr.com/madame-b-black-widow-role-mcu/
