4. Scarecrow Section
Batman has only come across Scarecrow in Arkham Asylum and it was a freaky hide and seek style part of the main mission. In Arkham City you can find evidence that alludes to him returning but you never meet him again. This could be Batmans first encounter with Scarecrow and the effects of his gas could be ten times more powerful than when met in Arkham Asylum, considering Batman probably hasnt been through this kind of mental torture this early in his career it could make for interesting playing. The side mission could revolve around a spate of influential people who had no previous mental issues going crazy and ending up in Arkham Asylum. Batman would investigate and find clues about the fear toxin gas which leads him to where Scarecrow is manufacturing the chemicals. A big battle could ensue with Batman in a terribly warped nightmarish world using everything he has to escape. The gameplay would have to be different to the instance in Asylum with a more in depth look at Bruce Waynes fears and his time as a child, if done right it could open up the origins of Batman in a way that has yet to be tackled in a video game.