Kane, you wake up one morning with a tiberium mutation and the scrin coming a knocking, or maybe isaac i can imagine that
ME: what the hell man I AM NOT A NECROMORPH, please stop trying to shoot my limbs off, it' a hallucination
ISAAC: ...
Me: Ahh! my arm
or actually, since there's some cthulu games, and the original alone in the darks were based on it, i'd have to say cthulu
ME: AHH! your shoggoth is eating my arm
CTHULU: blargy blargy blargy blarb
ME: ahh your eating away at my precious sanity points.... Gibber
finally any human from warhammer or 40k would be bad, but i think i could live with a dark elf, i mean aside from the whip fetish and the soul sucking and several other things that may cause discomfort i see no downside