Counter-attack

Overview
In melee combat, those Templars and enemies that are trained to fight in close-quarters may generate Counter-attacks. For Templars, only the Captain, Berserker, and Paladin will make Counter-attacks. For enemies such as Terrox, any that use a melee as their primary attack can also make Counter-attacks. Note that this indicates you are safe from Counter-attacks from ranged monsters like Spitters, if you can close to melee range with them.

Counter-attack charges are how many counter-attacks may be performed during the enemy's turn. Typically this value is 2 for each unit, unless modified by a particular ability or piece of equipment. Once these charges are depleted, no further counter-attacks can be performed by this unit until the subsequent turn. ("Counter-attack charges" is not terminology present in the game, but is used here to explain how counter-attacks work.)

Counter-attack charges are not required during the turn of the attacker, yet the attacker can counter-attack a counter-attack. When this happens, 2 AP is consumed instead of a counter-attack charge. If 2 or more AP is not present, a counter-counter-attack will not be possible. An exception to this rule is if an ability is active or a relic is equipped that permits unlimited counter-attacks. If this is the case, no AP/MP will be consumed during a counter-counter attack, giving a templar faced with this situation more options with how to end his/her turn.

There is a talent for the Berserker (Wrathful Defense), along with a tactical wargear relic for Captains & Paladins, that raises the cap on the number of counter attacks possible.

Sources of Counter-attack
A Templar or Xeno parries or blocks an attack performed at range 1.
 * The attack will need to be performed adjacently to the defender, which is always the case with melee attacks but counter-attacks can be triggered by blocking ranged attacks performed in melee range.
 * This is typically the most likely source of counter-attacks as auto-block can be easy to boost and has a 100% chance to counter, supposing counter-attack charges (or enough AP) remain(s).

A Templar or Xeno is hit by an attack performed at range 1 and the Templar or Xeno has > 0% counter-attack chance.
 * Follows the same range/resource requirements as above, but a roll on a d100 must be made as well. The roll must be beneath (or equal) the counter-attack chance in order for the counter-attack to occur. This is a fancy way of restating the percentage chance to counter-attack.
 * This is far less common, and is a feature of the Berserker class in particular.
 * Typically, gear boosting auto-block is more valuable than counter-attack boosting gear because the former implicitly grants a counter-attack chance via blocking anyway.

Tactics
Counter-attacks use the left-most (or top-most in the talent upgrade screen) talent. If a templar has a significant chance to counter-attack, through whatever mechanism, improving this talent can be helpful to making those blows land and deal decent damage. Heat cost is still applied, but those talents are inexpensive so it usually isn't a major concern.

Enemy counter-attacks are a real threat. While most (all?) melee enemies have some % chance to counter-attack even upon being hit, the main threat is when they parry attacks as this will always trigger the counter-attack (assuming charges remain.) This gives additional importance to not attempting low-accuracy attacks in melee range.