A Lego Batman: Legacy of the Dark Knight FAQ says there will only be seven playable characters in the upcoming game.
One of the highlights of Gamescom Opening Night Live had to have been TT Games finally revealing their long-rumoured follow-up to Lego Star Wars: The Skywalker Saga in the form of Lego Batman: Legacy of the Dark Knight. While not specifically adapting any one film, game, or comic, the game pulls segments from Batman's history, such as the combat and open world stylings of the Arkham games, and segments from films like The Dark Knight and The Batman in a "story-led campaign from origin to legend".
