Who is Diesel from Visions of Sugar Plums and what is their importance?

Diesel is a man of mystery. Popping into Stephanie's kitchen out of the clear blue doesn't seem to surprise this man who claims to have some supernatural powers, although he is never clear on the extent of those powers. The most Diesel will say is that he has been sent to help. Powers include being able to pop in and out, of various locations, an uncanny sense of his surroundings, and the ability to unlock any type of door with the touch of a hand.