Adrenaline speeds up health regeneration so you recover faster between exchanges. It is a level 5 Combat skill costing four points.
Adrenaline sits at position 17 of 18 in the Combat tree. Unlocking Adrenaline takes 4 skill points. You need level 5 before you can buy it. Jacob and Evie each have their own skill tree, so you buy Adrenaline once for each twin.
Combat Stamina
Multi-Kills restore health, more for each enemy killed.
Counter
Press the counter button as an enemy swings to turn his attack back on him.
Counter Boost
Counters get a wider timing window and deal more damage.
Execute I
Stun an enemy with Stun Attack, then use a Tool Combo on him to execute him outright.