Primal Innate Spells DC 14, attack +6; 1stillusory disguise
Hidden Movement If the umbral gnome scout starts its turn Undetected or Hidden to a creature, that creature is Off-Guard against the umbral gnome scout's attacks until the end of the turn.
Source: Pathfinder Monster Core
Running this fight? Add the umbral gnome scout to the initiative tracker: type its name and the AC, hit points and Perception for initiative fill in, and the book button shows this stat block mid-fight.