Eidolon's Opportunity Feat 6
Source Pathfinder Secrets of Magic
Trigger A creature within your eidolon's reach uses a manipulate action or a move action, makes a ranged attack, or leaves a square during a move action it's using.
Your eidolon makes a melee Strike against the triggering creature. If the attack is a critical hit and the trigger was a manipulate action, your eidolon disrupts that action. This Strike doesn't count toward your multiple attack penalty, and your multiple attack penalty doesn't apply to this Strike.
Traits
Anything that doesn't list another rarity trait (uncommon, rare, or unique) automatically has the common trait. This rarity indicates that an ability, item, or spell is available to all players who meet the prerequisites for it. A creature of this rarity is generally known and can be summoned with the appropriate summon spell.
EidolonA creature with this trait is a summoner's eidolon. An item with this trait can be worn by an eidolon. An eidolon can have up to two items invested.
SummonerThis indicates abilities from the Summoner class.