No comment goes without reply, and neither does an attack.

When attacked with a melee attack from an enemy within your melee range, as a REACTION you may attempt to parry and counter the attack.

ROLL OFF!: Roll to beat the DM's attack against you. Roll a D20 add your attack modifiers as normal. if your total attack roll beats the opponents initial total attack roll, you take no damage to yourself and may roll damage against your attacker. If you fail to beat the attackers roll, you fail your attempt and take damage as normal.

High Reward, High Risk: If you are successful in the ROLL OFF, and your roll was a natural 20, deal critical damage as normal. If you fail in the ROLL OFF and rolled a natural 1, you open yourself up to your opponent and suffer double damage. THIS STACKS WITH ANY CRITICAL HITS YOUR OPPONENT MAY HAVE ROLLED. this means a botched roll can result in 4x the regular damage.

Stand off: if your challenge roll MATCHES the DM's original Roll, you Parry the attack TAKING NO DAMAGE, and DEALING NO DAMAGE