Alright, here's the Power in list format.
UNLIGHT [-5]
Description: In a real world, physics-grounded Universe, darkness is simply the absence of light. Bring a light into a darkened room and the darkness recedes - it has no power to resist. The power of the Unlight is another matter.
Sponsor: Unlight is one of the powers offered by one or more Old Ones, the forgotten gods in the Outside. Even seeking knowledge of this power is a violation of the Seventh Law, as is every use of it, regardless of how benign it might seem. This is a very quick road to self-destruction.
Agenda: Unlight seeks to destroy things, especially things that keep the Outside from coming inside.
Evocation: Evocations cast with Unlight destroy things. They resemble darkness and cold evocations.
Thaumaturgy: Rituals cast with Unlight can disrupt, destroy, and decay things. They can also open holes in space-time to allow for world-walking effects, but this tends to be bad for reality as a whole.
Evothaum: All rituals that may be cast with Unlight may be cast with Evocation's speed and methods.
Extra Benefits: Unlight can harm characters with Physical Immunity as though they had Mythic Toughness. Moreover, any Unlight spell that is used to block or destroy matter or energy gets two free shifts of effect added to it after casting. Double this bonus to four free shifts when Unlight is used to block or destroy light or heat. Reduce it to zero free shifts when Unlight is used against magic infused with Soulfire.
Drawbacks: A character who fails to control of an Unlight spell must take their margin of failure in both backlash and fallout. The sponsor will never help mitigate this effect.
Everything look good? I removed the Nevenever/material distinction because you said it was unnecessary.