Combined with a high rank Reflex Guard, Parry will allow you to automatically stagger melee enemies, but only if you are channeling at the moment of the parry.
Radial Disarm will remove any ranged weapons from enemies, making this strategy effective against all enemies except Ospreys.
Special attacks will not be parried successfully, although they will be blocked. A Grineer Scorpion's grappling hook and any heavy unit's Seismic Shockwave knockdown attack will be blocked but not cause a Parry. A Shield Lancer's shield bash cannot be parried, and will push you back a short distance, but will NOT knock you down since you were blocking.
Added in Update 10.0. During Melee 1.0, it granted a chance to knock down a melee attacker while blocking.
As of Update 13.0, the Parry mod will only work if one is channeling while blocking against melee attacks. When successful, a counterattack will be initiated, which momentarily stuns an enemy and allows them to be killed using a melee attack prompt similar to Stealth Attacks.
In Update 17.0, the counterattack maneuver can be performed by anyone who activates channeling immediately before blocking an attack, reducing the necessity of this mod for melee-oriented players.