From what I am seeing so far, Mobyss (Sooth), Savadrill (Cartoons!), Malarichtr (FlareBlitz), and Colosoil (franky) seem to be my cup of tea and names that I would vote for. I find that they flow very well so I don't have to feel awkward about saying the name. They are also quite fitting for this fellow.
Since a lot of people seem to be throwing around suggestions, I might as well toss a couple more into the jumble as well.
Sinister + Monodon monoceros = Siniceros
The word "sinister" comes from this narwhale Pokemon's dark type, hence why I used that in this name. Monondon monoceros is the species name for the narwhale, so I just tacked on "ceros" onto the end.
Subterranian + Scar = Subterscar
The word "subterranian" comes from the fact that this Pokemon is peeking his head out of the ground and, hence, goes under ground. It's also dark underground, I would imagine, but that's beside the point. The "scar" part comes from the fact that there are scars on the narwhale's body.
I'm open to suggestions as to adjusting the spelling of either name or which name I should go with for my final submission (if I make one, that is).
Edit:
@ The Other Doug: I'm glad you like "Siniceros." Since you comented on one of mine, I might as well give you some feedback on one of yours. Regarding Terrawhale, I didn't even realize that the "terrible" part was in there, so I think you should bring out the "terrible" more. Maybe changing the name to "Terriwhale" might do it, but that's purely my suggestion and, therefore, at your discretion.