Successfully performed an event attack on a Pacifista.
Only possible in the prologue of the main log at the end of the stage when you face of against a Pacifista.
When he has one bar left you need to stun him. After he is stunned (when stars appear circling around above his head) an R1 sign above his head will also appear. Get close to him and press R1 then Down and X, hold LS down and RS down,X, square repeatedly and finish it of with circle.
You can stun an enemy by landing a combo when he has that yellow sign above his head. You could also equip the coin combo: Mr 2, Magellan, Transponder Snail which increases the chance to stun enemies.