The "Unlaboured Flawlessness:" players who are skilled enough to stay alive at 15% health can cut enemies down with this weapon at shocking speeds. On the other hand, given the strict health requirement and the game's difficulty, this isn't as severe as the others listed.
The Izuna Drop is fairly easy to execute and will instantly kill any human-sized Mook at lower difficulties: in the first game, enemies often block and players can only perform the technique with "katana-like" weapons, making its use restricted. However, the sequel ensures almost all weapons have access to an Izuna Drop of one form or another, and enemies don't guard at all from it. Rectified in Sigma II by Nerfing it slightly via making some Mooks (almost all of them on Master Ninja difficulty) resilient enough to survive it.
The Flying Swallow was overpowered in the original version of the first game, to the point where it would make short work of enemies and even some bosses; the Final Boss could even be cheesed by simply spamming it. Addressed in Ninja Gaiden Black where as the Flying Swallow was Nerfed extensively: enemies and bosses could now block it, and they would do so more often on harder difficulties; Black even goes so far as to include enemies that punish players for relying on the technique too much.
"Ultimate Techniques" are a similar case: in the first game, without absorbing essence to speed it up, it takes several seconds to charge a full-powered Ultimate Technique and their effective range is limited. In Ninja Gaiden II and Sigma II, it takes half the time to activate, with some weapons' Ultimate Techniques being glaringly over-effective on large groups of small Mooks.
The "Hurricane Packs" for the modern Ninja Gaiden added an "Intercept" maneuver where Ryu can parry any enemy attack and trigger a Counter-Attack via Ultimate Technique if players can get the proper timing down. It's no wonder Intercept's effectiveness wound up being removed in Ninja Gaiden Black.
The "Eclipse Scythe" in III, despite its slow attack speed, can become this if used properly. With the Dragon Sword or the "Falcon's Talons", players can directly repeat successful Steel-on-Bone attacks on nearby enemies. The scythe, however, has the longest reach of all available weapons in the gamenote The scythe and claws were Downloadable Content in III, meaning "nearby enemy" entails into "any enemy within a large, encompassing radius". As long as players don't screw up the initial Steel-on-Bone strike, taking down entire waves of Mooks can be done almost effortlessly. As of Razor's Edge, the scythe has taken this completely, being the only weapon used by players more than the Dragon Sword against groups of Mooks. However, it suffers from a few drawbacks, notably a limit to the number of successive Steel-on-Bone attacks thanks to ''Razor's Edge" rectifying game-play and the inertia after every regular strike of the weapon.
Speaking of the revamped Steel-on-Bone system in Razor's Edge, provided players take the time to properly use it via Counter Attacks, Mooks bum-rushing players will mean nothing if players can spot the tell from enemies that allows a Steel-On-Bone to trigger. Furthermore, having low Hit Points won't mean a thing either since successive Steel-On-Bone strikes also grant Regenerating Health.
