The wight: a humanoid undead that mysteriously arises from every creature slain by negative levels, even those with smaller bodies, larger bodies, nonhumanoid bodies, or no bodies at all. It's not entirely sure how tiny air elementals can turn into these, but necromancers aren't complaining.
4 undead RHD aren't a great starting point, and the stat array isn't noteworthy either. The racial bonus to move silently is useful, I guess, as it's one of the only skills to spend your RHD points on. An 1d4 slam attack is less impressive, though the negative level it carries is pretty neat.
A wight's main ability is going to be its near-limitless spawn creation potential. Given the obvious imbalance of an army of level-draining undead at ECL 4, I will be ignoring the ability. With that in mind, a LA of +0* should be balanced enough.