You can use your invisibility psi-like ability more often.
Prerequisites: Duergar, invisibility psi-like ability.
Benefit: You can use the invisibility psi-like ability granted by your duergar heritage a total of three times per day.
Normal: A duergar's invisibility psi-like ability can only be used once per day.
Special: You can gain this feat multiple rimes. Each time you take the feat, you gain two additional daily uses of your invisibility ability.
Source: Complete Psionic, page 49.