The PES 2021 ML editor is a built-in feature that enables users to modify and customize various aspects of the Master League mode. Master League is a popular game mode in PES 2021 where players can manage their own team, make transfers, and compete against other teams in a simulated season. The ML editor takes this experience to the next level by allowing users to tweak and adjust a wide range of settings, from team stats and player abilities to league structures and tournament formats.