That would explain his immortality, knowledge of what we need before we need it and if you pay attention MC starts acting more like Shady in later books but that might just be him rubbing off on him. Last update if I remember MC said something about selling stuff and then said "something something Im starting to think like Shady". Also in bk4 slave Shady needed you to grab him 4 elements stuff, that might have been because hes in a normal body? That could all just be red herrings though.I think Shady is the MC, and the last chapter is you going through the whole game as Shady reaping the benefits from going through already.
This gave me an interesting theory idea, what if MC splits like the snake lady did and the different routes are caused by which Shady got to influence events?