Could a monster be made both weak AND powerful at the same time?

[Jear77]

I have a question about making an enemy that is both weak and powerful at the same time. I'm running a d20 modern game setin the 1920s with sanity/ horror/ madness/ taint rules that's a combination between Call of Cthulhu and Ravenloft Masque of the Red Death. I was wanting to create a bad guy that is both super weak and unbelievably strong at the same time. What I had in mind was a combination of entities: an undead monster "rolling shadows" that solidifies and creates tentacles which wrap around the victim dragging them into their doom, typically in alleyways. It feeds on the horror of the person being dragged. Strong light causes it to flee, and an ancient substance known as "chimefire" will destroy it utterly (it knows where a source of it is.) Generally, it will attack any lightsources in the area or use its specail ability to create darkness. The other half would be a "flesh" monster which it could be in symbiosis with, while weak in and of itself, the combination of the two would be too difficult for a 5th lvl party to defeat. Any ideas on stats? Any help would be helpful. Thanx!

[freyar]

I'd help, but I'm afraid I can't get a good picture of what this thing is like....

[kinem]

So basically, there are two monsters - one powerful and one weak - and killing either one leads to the death of both? Sounds like it could work.

Maybe the "flesh" part could just be a low level human, and for some reason he is joined with the monster. If it's undead, maybe it's his spirit: he could have had a "near-death" experience in which he actually did die, but doctors were able to revive his body. His normal looking living body still holds his undead spirit tied to the material plane, but it can roam several yards away from him.