This is a Monster — a class feature gained through that class's own talent choices, not a feat you pick through normal feat selection.
Choose one of your spell-like abilities, subject to the restrictions described in this feat. You can use the chosen spell-like ability as a fearsome spell-like ability three times per day (or less, if the ability is normally usable once or twice per day). When a target takes damage from a fearsome spelllike ability and fails its saving throw against the spell-like ability, it becomes shaken for a number of rounds equal to the spell-like ability's equivalent spell level. If the spell-like ability doesn't allow a saving throw, creatures harmed by it can attempt a Will save (against the DC that the spell-like ability would have if it allowed a saving throw) to negate the shaken effect. If the effect of the spell-like ability also causes targets to become shaken and a target fails its saving throw, the duration of the shaken condition caused by this effect stacks with the spell-like ability's. A fearsome spelllike ability can't cause a creature to become frightened, even if that creature is already shaken. You can only select a spell-like ability duplicating a spell with a level less than or equal to 1/2 your caster level (round down) -2. For a summary, see Table 3-1. (page 79) [Special] This feat can be taken multiple times. Each time it is taken, you can apply it to a different spell-like ability.
Prerequisites
Spell-like ability at caster level 6th or higher