As an addition to Sound Manipulation, The Lich quite often makes inhuman noises in different vessels (
Mortal Recoil as one example) and could talk as a skeleton in
Escape from the Citadel.
I think he should have resistance to Toxins and Radiation. In
Mortal Recoil (s)he drank a mixture of gasoline, lighter fluid, bleach, and plutonium, with the result only making him stronger. Speaking of which, this could give him statistics amplification, as he shows consistently that he can do this to get to full power (P.B described it as such).
He could have Biological Manipulation or Transmutation. His darkness spread throughout the Citadel, "breaking cats (prisoners) out left and right. Turning cats grey." One prisoner not only became gray, but also formed multiple mouths, although it's possible it already had this power and the closed mouths just aren't visible on it, as many of the characters retained their abilities after being turned, such as a Void Caster.
Escape from the Citadel. The effect even wears off when he's turned into a person.
It's not shown on screen, but he could potentially have explosion manipulation. His crystal exploded (or appeared to based on the large amount of light, sound, subsequent shockwave, and large amout of smoke not just emanating from the fire), releasing a large amount of black flame.
The scene is at 17:22, so you can judge for yourself.
