Craniac, Shadows is designed to be a completely standalone game. You can play it without anything from the core box (and in fact, I actually have not combined anything from the two games yes). There are a couple of things in the rulebook that are NOT in the Shadows box and I think Shadows did not, inexplicably, come with a grenade blast template. But yes, you can get just it and go from there. It's easier to get into the system that way, I think, because there's only one non-essential expansion for that side of the product line to date.