Up to +5-20% Strength based on the charge time of your heavy attacks. Stacks 3 times.
+5-8% Strength for 4.5s on Kill. Stacks 5 times.
Up to +14-20% Damage on Hit (Staggered Enemy), scaling with Stagger.
+14-20% Strength for 5s when every pellet in a shot hits the same enemy.