Fan Casting Characters who could've been in Gotham

You know how Smallville had characters like Aquaman and Green Arrow? Well, what if Gotham had been the same way? Keep in mind I'll only use characters who could have fit into the world of Gotham, so don't be triggered when I don't have Green Lantern on here, okay? Also, please add descriptions with your suggestions, telling when they would appear, what they would do, and their realtionships with other characters.