help? Please? (1)

I tried to stay away, but what type of characters should I introduce in Moonlit Eyes? and how would they be found? If you've read any wings of fire, you will remember Peril who showed up as the "Overpowered Enemy". But I also want to add a twist character like in Undertale with Flowey and Asriel or Wings of Fire with prince Hailstorm and Pyrite. Tell me what you think!