Mastery of Twisted Shadow

(Player's Guide to Eberron, page 126, DnD 3.5)

[General]

You gain the ability to reach into the Plane of Shadow when casting an illusion, concealing yourself in the raw shadowstuff drawn forth.

Prerequisite

Knowledge (the planes) 2 ranks, Spellcraft 4 ranks

Benefit

Whenever you cast an illusion spell, you can choose as a free action to grant yourself concealment for 1 round per level of the spell. Multiple uses of this feat don't stack; only the longest duration applies.