Increased Cleave and +5-20% Heavy Melee Attack Damage on Energised Attacks.
+1-2 Extra Chained Energised Hits and +2.5-10% Impact on Energised Hits.
+2.5-4%Charge Speed on low Overheat. Stacks up to 5 times.
Critical hit chance scales by your current heat level up to 27.5-50%. Also increases critical ranged attacks damage by 4-10%.
With "Focus Target" (Bottom Middle Keystone) and it's branch for "Redirect Fire!" you can keep the 8 stacks of 1.5% dmg up constantly if you keep tagging and killing the targets. It is easy to do because the buff for Redirect Fire lasts 10sec which is pretty generous.