Honestly, I just don't think Darkness needs this card, or should get it. At least not in this point in time, with the other elements like they are. Course, it's a pretty awesome card, but being realistic it'd make Darkness even more powerful. Darkness has steals, Devourer/pest, Vampires for healing, Siphon life for creature control, it doesn't need an immortal creature that also has momentum without a splash.
That's not to entirely shoot down the idea, and I doubt you were expecting it to actually be used now, just thought I'd be the one to say it before someone else did.