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 sickening spell-like ability three times per day (or less, if the ability is normally usable only once or twice per day). When you use a sickening spell-like ability, a target that takes damage from the spell-like ability becomes sickened for a number of rounds equal to the spell-like ability's equivalent spell level. If the spell-like ability allows a saving throw, a successful save negates the sickening effect. If the spell does not allow a saving throw, the target can attempt a Fortitude save (against the DC that the spell-like ability would have if it allowed a saving throw) to negate the sickening effect. If the effect of the spell-like ability also causes targets to become sickened and targets fail their save, add the duration of the sickened condition caused by this effect to the duration of the sickened condition imposed by the spell-like ability. Spell-like abilities that do not inflict damage do not benefit from this feat. 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 on p79. [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