Complex sentence: Toad then calls the bartender Mr. Winky as a witness to the agreement; but much to Toad's surprise, Winky claims that Toad had tried to sell him the stolen car.
Split into simpler sentences: Toad then calls the bartender Mr. Winky as a witness to the agreement. However, much to Toad's surprise, Winky claims that Toad had tried to sell him the stolen car.