The artbook says, "It was an extremely small colossus. You'd defeat it by menacing it with your bow, then drawing closer while hiding in the grass and attacking from behind. I imagined the battle with Devil to be fierce. You'd hide in the grass and jump on its back."
Although the location Devil would be fought is unknown, the most plausible speculation places the colossus at quadrant H2 on the map, due to the orange-brick structures seen in the pictures' background being similar to the ruins by the Beta Dam.