Shadow Energy (3.5e Equipment)
From D&D Wiki
A shadow energy weapon has its significant portion transformed into shadow, although this does not modify the item's weight. Only while held the weapon is under the continual effect of a darkness spell. A shadow energy weapon ignores nonliving matter. Armor and shield bonuses to AC (including any enhancement bonuses to that armor) do not count against it because the weapon passes through armor. (Dexterity, deflection, dodge, natural armor, and other such bonuses still apply.) A shadow energy weapon cannot harm undead, constructs, and objects. This property can only be applied to melee weapons.
Strong transmutation; CL 16th; Craft Magic Arms and Armor, gaseous form, darkness; Price +4 bonus.
Notes: If you use use the 3.0 version of 'Darkness', you should still use the 3.5 version for this effect, as in lowering light levels by one step and 20% concealment. The concealment shouldn't be overpowered when used as melee weapon because both combatants normally suffer the miss chance unless extra steps are taken. And yes this effect is just like Brilliant Energy. I just thought Brilliant Energy needed a counterpart like Unholy to Holy.