What Do You Think?

This is basically a post about a fanfic idea I have. It's about Twilight being infested by a demonic parasite called a Mara. This creature had dwelled in her subconcious mind for some time, plaguing her with nightmares. Without a good night's rest, Twilight gradually becomes sicker. She knows something is wrong, as she begins to feel like her sanity is slipping. Eventually she collapses into a coma state.

Cue the main story and my question for you guys.

I actually started thinking of this plot because I wanted to write for an OC of mine called Sir Sortilege. In the story, he and Princess Luna enter Twilight's mind to try and find the demon that in creating and feasting on her nightmares. The Mara is aware of thier presence, and hides its location by producing nightmare after nightmare for our heroes to wade through. Luna, the dream guide for Sortilege, helps to find doors for them to cross through, and into the next layer of Twilight's mind. Meanwhile, in the waking world, the changlings have come for another attack. Sensing Twilight incapacitated and the Elements of Harmony useless, the Changling Queen attacks Ponyville and tries to strike the unicorn down for good. Her friends won't have any of that!

My question is...Should I even bother with the OC? I ask because I think I can just as easily eliminate him and make it so that Luna is THE hero of the story. Thing is...I kinda like the plan I have in store for him. But I know how many people avoid OCs like the plague...So what do you guys think?

(I was also thinking of having Twiluna and ApplePie undertones in it. But it isn't a main focus of the story.)