In my story which has a 12 year old as the main character, he meets someone who is thinks he's Satan. He's gone as far as to make his house look like hell, got a few skeletons around and chains, ect. But I want the reader to be given a choice if they think he is actually the devil. I want it to go either way, have it a bit of a mystery. What would the best way of doing this be?
Go for subtle. whenever he is in the room, there's a smell of burned mathes or smoke. He's very persuasive, but somehow no one feels comfortable in his presence either. He seems to disappear or reappear when people aren't looking. He lit a cigar, but you could swear he wasn't holding a lighter... Little things like that are much more effective than chains and skeletons. And don't pile up the little things either. Keep a light touch.
As an extension to Cogito's post, symbolism can be helpful as well. Most people listen to Satan rather than God(and end up doing a bad deed), yes? So you put in a character that's all good and holy(remember, apply Cogito's advice), then have people ignore what he says and listen to Mr.I-May-Or-May-Not-Be-Satan. Or perhaps there's a trident over his fireplace, or the deer head over his couch looks just a little too terrified...
Make him a smooth talker. All other details are irrelevant. Avoid fire and brimstone. In almost every work of fiction that Satan or devils have appeared in from Faust to Ghost Rider, they have been smooth talkers and great salesmen. Satan's primary goal is to tempt humans over to his side so he would try to make himself seem as nice and charming as possible. Having said all that, a cloven hoof here or there wouldn't hurt.
Smooth, mysterious characters should do the job fine, don't go for the whole out there leaving items Around the house.
