Pack Tactics fires on summon hit. On a piece that carries it it reads: Summon hits build Pack Tactics: +{value}% Summon Damage per stack up to {count}, fading 4 s after their last hit.

Word for word it is Summon hits build Pack Tactics: +{value}% Summon Damage per stack up to {count}, fading 4 s after their last hit, and the number in it grows with the gear: 1 to start, 0.02 more for every item level, and it only goes off every 10 times you set it up.

0 bases carry it.