Cloak of Shadows (3.5e Incantation)
From D&D Wiki
Level: Swordmage 2
Target/Area: 20 ft. circle centered on the caster
Number of Attacks: None
Duration: 1 round
Saving Throw: None
You darken the arcana around you, causing it to become pitch-black. You create a 20 ft. area of darkness around you. Everyone in the area gains partial concealment (20%) until the end of your next turn.