I'd note that a primary conceit of the Harry Potter series is Harry and his friends figuring out whatever big mystery crops up each year. So Doug coming across as a bit mysterious isn't really a problem. You've already got the Gryffindor group comparing notes on Doug as they try to understand the odd and amazing things he does, so use their PoV to slowly reveal more of Doug's past. I'd be happy if they only get a complete reveal towards the end of the Step, with Harry making the intuitive leap that 'Doug is a superhero from another world' and getting Doug's confirmation while Hermione squawks in outrace over such a nonsensical explanation actually being true.
“I really hope I’m behind this convoluted mess; at least that way I’ll be able to get revenge by doing this to myself. I won’t even have to feel bad because it’ll be all my fault.” - Harry Potter, The Master of Death by Ryuugi.