Overview
The first one can be encountered in FC World B. There has 1/6 chances that he appears in the place that the entrance was surrounded by 6 pyramids, if you equipping Demon effect and enter the entrance he will always stay in that place. He teleports you back to the FC Basement, right next to the second FC Demon.
The second one can be found inside FC Demon's Room in FC Basement. The Demon Effect can be acquired by interacting with him.
FC Demon resembles a traditional japanese Oni due to his red color and horns. Two versions of him exist.