One of the pieces of concept art on the last page of the art section has a picture featuring Ms. Splosion man talking into a walkie talkie along with her making an angry face and her being happy. The description says it is used in another game, but it tells the player to guess what it is. Does anyone have any idea what it could be from? I have no idea. They look like pictures that would be next to a text box.

Maybe gunstringer?

I don't think it's Gunstringer if they said it's used in another game. 
Maybe if it said, it's being used in another game.