Lesser Invisibility

Lesser Invisibility allows the Succubus to become invisible for 5 minutes. Any command given to or damage taken by the Succubus will take her out of invisibility mode. Unlike the Imp's Phase Shift ability, this does not prevent the Succubus from setting off traps or being hit by area-of-effect spells and attacks. The Succubus cannot become invisible during combat, although if she is invisible when combat begins, she can remain invisible until she takes action (or is hit by AoE damage).

This ability became auto-castable in patch 1.7. The AI will keep the Succubus invisible whenever possible. It recasts itself when Lesser Invisibility runs out or when the Succubus leaves combat.