My $0.02: Something is OP when, and only when, it is able to consistently perform outside its intended role and/or interferes with established game mechanics. The two examples that come to mind for D2 are Omolon 450 Autos and the Nightstalker Invis issue. Omolon Autos are OP by the above definition in that they consistently perform outside their intended role. Autos are, by design, intended for CQ combat, and their high RoF is offset by limited range and increased recoil if the trigger is held down...but Omolon Autos are not effectively affected by either, thus allowing them to do more damage than intended at impractical range, and allowing them to stay dead-on target longer than any other weapon. In the case of Uriel's Gift, HCR interferes with the ability of an opponent to acquire a target to even fight back, even if it's a Scout player at mid-long range - I have a hard time believing any Auto was designed specifically with the intent of being able to wear down a ranged player with body-shots while disallowing them from effectively returning fire. Nightstalker Invis is presently OP by the above definition in that it directly negates a necessary game mechanic in PvP. Whether it's noticed or not (for me, it definitely is), PvP combat relies heavily on Aim Assist to acquire targets and correctly register hits - if you pay close attention, you can actually feel/see the reticle "snap" to enemies once the reticle gets close to them ADS (and resists pulling away), and the right thumbstick gains slightly finer control to allow precise aiming and consistent target acquisition. In the absence of a valid target, weapon handling becomes much "sloppier/looser," and landing shots (both initial and follow-up) becomes significantly more difficult. Since Nightstalker Invis negates Aim Assist and the game treats them as a non-target, it breaks the normal rules of engagement and allows Nightstalkers to approach and specifically use CQ weapons (especially Shotguns and Swords) or melees without an effective counter.