Introduced in Build 124.0, the Ninja is the first katana class, the first katana class available to players, and was the only katana class for over 5 years. Ninjas are also the first class to have two seperate ability functions (speed & damage) in one. In addition to various katana buffs over the years, Build X.31.4 increased his VIT cap.
Along with Samurai and Kensei, the Ninja is now one of three katana classes. With an attack range smaller than the dagger, Ninjas are effectively a melee class - but a high speed class that wears the lighter leather armor instead. Unlocking him requires attaining level 20 with both Rogue and Warrior. See his stat gains, caps and averages here.
Ninjas stand out with a 70 ATT and DEX cap; just below the Wizard in effective stats. With an above average SPD of 60, Ninjas move around quickly, only boosted by their ability. But despite their close range, Ninjas only wear leather and have the low-for-a-melee DEF cap of 25. As another ‘glass cannon’, Ninjas rely on their dodging, DPS, and speed in order to be successful.
The Ninja’s weapon of choice is the katana. Katanas are essentially swords, exchanging damage for a somewhat longer range and the ability to pierce enemies. But an average Katana’s range is still quite small, making it more difficult to damage dangerous enemies. While Ninjas have amazing offensive stats, their weapon somewhat holds back their actual DPS.
Tiered Katanas are basic options for any Ninja.
The Sadamune is the best tradable tiered katana, able to pierce multiple enemies for high damage. The Masamune isn’t too far behind, while the T14 Kusanagi 
is a prestigious drop from Oryx the Mad God 3.
The Doku No Ken (Doku) is a very practical, tradable katana for the Ninja. It has a superior range (5.2 tiles) while outdamaging the Sadamune until a decent DEF. This damage comes from a large poison AOE that detonates every 3 seconds. The only downside is the wavy pattern; firing like a staff, the shots line up at the middle and end. It drops from The Crawling Depths.
The Celestial Blade is an upgrade to the Doku against single targets. Its firing pattern is even odder, with shots that only really line up at the end of the 5.2 tile range. It also loses piercing and the poison burst. In exchange, the Celestial Blade is very powerful, even outdamaging the Kusanagi. It is a midgame drop from Feargus the Obsidian Dragon.
The Ray Katana sports an even higher 6.2 tile range, at the cost of weaker (albeit consistent) damage than the above katanas. It is an event god drop, specifically from the Rock Dragon.
The Void Blade is an odd katana; its extreme damage, slow firerate shots take a while to actually start accelerating. Impractical for standard use, it can be ‘prefired’ against any boss with invulnerability phases to get more shots in. It is a tradable katana that can be found in the Toxic Sewers.
The Kazekiri is the ST katana part of the Akuma Slayer set. It fires two shots that pass through obstacles. Like the Doku, the Kazekiri’s shots have a curve, truing up at the end of their range. While the reduced range is a hinderance, it is effective in fights that occur on terrain with plenty of obstacles, like most realm encounters. This katana is dropped by Daichi the Fallen.
These endgame katanas are the best of their class.
The Enforcer fires 2 shots, like a much tighter Demon Blade. Enforcer’s true range matches up with a tiered katana (with even higher actual range), making it a go-to for all sorts of situations where DPS is useful. The only downside is that it doesn’t pierce through enemies. It drops from Chief Beisa.
Valor is another endgame katana, this time from The Bridge Sentinel. Outdamaging the Enforcer at most DEF levels while also piercing enemies, its downside is the -10 ATK penalty when firing In Combat, leaving it outdamaged by other top-tier katanas.
The Ninja’s ability, the star, has two entirely different effects.
Tiered stars give 
Speedy, which allow the Ninja to be one of the fastest classes in the game. Most stars, similar to Quivers, have an extremely high range; useful for sniping against dangerous opponents. Unlike most quivers, most stars do not pierce enemies, so aim carefully.
The Doom Circle and Dynastic Star are the best tiered stars for damage, dealing the most of it and having the most MP-efficient damage of the tiered stars from a range of 15 tiles. Tiered stars don’t cost any more MP for Speedy, but due to the higher MP cost on release, are marginally less efficent at buffing.
The Spider Shuriken only drains 5 MP/second, half that of tiered stars, and is cheap to throw. Therefore, it’s the most efficent star for the Speedy buff, useful when damage isn’t required. On top of that, its shot also inflicts 
Slowed. This star drops from Arachna the Spider Queen.
The Midnight Star inflicts 
Paralyzed on an enemy for 4 seconds, but with significantly lower damage. Use this star when there’s no other paralyzing classes around, assuming enemies are even vulnerable to it at all. This star drops from the Ivory Wyvern.
The Kageboshi fires 4 boomeranging shots, forgoing any status or hold effect for pure damage. However, it only has a range of 6 tiles, and an uncomfortably close 2.35 tiles in order to hit all 4 shots. Because of this, it is recommended to use this star if you are confident in your dodging skills or when damaging single targets. It is a rare drop from the Jade and Garnet Statues.
Rage Claws is a practically limited edition star with a similar function to the Kage. It fires a wide burst of shots, reminiscent of Wakizashi, dealing lots of damage, even though it is very hard to hit all the shots on one target. It again has no held effect, but has a 1/3 chance of providing either +15 ATT or +15 DEX. This makes it a great star for clearing and close-quarters combat.
The Star of Enlightenment inflicts 
Berserk and Slowed at the increased cost of 20 MP/second. Slow might be helpful for dodging tight patterns from bosses like the Killer Bee Queen, and Berserk is quite a strong buff (if Warriors are not around). In addition, the actual star is stronger than any tiered star. Best used in solo play, this lategame star drops from the Crystal Entity.
The Daybreak Chakram features the same 20 MP/second cost in order to inflict the 
Armored status instead, which a group is less likely to provide. This star deals good damage, but weaker than the Star of Enlightenment, from a tiny range of 5 tiles. Nonetheless, Armored is an incredibly useful status on such a fragile class like Ninja. It is an ST item from El Dorado in the Secluded Thicket.
The Ballistic Star fires eight armor-piercing, parametric shots around the user. Four of them circle very closely, inflicting 
Stunned for 3 seconds. While being the best damage star, the odd shot pattern makes it only really suited for predictable enemies like the Crystal Worm Mother. And instead of providing a hold effect, the Ballistic Star gives 4 seconds of 
Healing when used; useful for activating the Centaur’s Shielding independently, or just for raw health when without a Priest or Paladin.
The Crystalline Kunai does not have an effect when held, nor does it shoot projectiles when pressed. Instead, it provides a +15 ATK boost for 3 seconds and has the reactive proc of shooting 3 projectiles when hit. It makes for a good close-quarters style of combat as it primarily boosts your katana’s damage. It is an ST star that drops from the Crystal Worm Mother.
The leather armors worn by the Ninja amplify his protection against enemy attacks and enhance his attack speed through increased dexterity.
Tiered armors: Hydra Skin Armor, Wyrmhide Armor and Leviathan Armor are the primary armors for the Ninja, providing ample defense and great dexterity boosts. You can never go wrong with a tiered armor.
These relatively cheap, tradable leather armors provide a slight speed boost for a slight decrease in other stats.
The Golem Garments are an ST leather armor obtained from the Lost Halls. This armor is essentially a far stronger, albeit much rarer version of the Spectral Cloth Armor. It trades the DEX for a massive +8 ATT bonus, being a good option (but not the best) for optimizing DPS.
The Armor of Nil and Vest of Abandoned Shadows are defensive UT leather armors. Nil gives the greatest raw DEF of any armor, while giving no offense and taxing speed. The Vest is more HP focused, but gives Armored for a short time when it, and a fairly large +15 VIT. Nil is better for avoiding In Combat thresholds, while the Vest is better for endgame dungeons where HP is important. Armor of Nil is from the Void Entity, and the Vest of Abandoned Shadows from The Shatters, both endgame items.
The Hirejou Tenne (Tenne) and Centaur’s Shielding sacrifice the majority of their DEF boost for an unrivaled increase in damage. Tenne gives a huge, unconditional +16 DPS stats. The Centaur’s gives even more if you have the Healing status, such as from the Ballistic Star.
The Turncoat Cape is an upgrade to the Beehemoth Armors. An armor especially suited for rushing, not only does it provide a massive +10 SPD, but whenever you get hit for enough damage, you will turn Invisible.
The Ninja specializes in being fast, and dealing massive damage. As such, the rings that a Ninja should wear must reflect this specialization or compensate for his lack of other statistics.
HP boosting rings in general are great for increasing a class’s survivability. The Ring of Exalted Health, Ring of Unbound Health, and Ring of Decades give massive boosts to HP.
The Ring of Unbound Defense, while an unconventional choice, can work as a defensive ring for the Ninja due to the class’s low DEF cap of 25. However, most would prefer HP rings as they are generally better for tanking damage.
These rings balance power and survivability.
The Ring of the Pyramid (Pyra) is the easiest to get - even being tradable. In addition to a respectable +100 HP, it gives a decent ATT and DEF boost. The Divine Coronation is a strict upgrade; providing more HP, DEF, and a superior DEX boost, in addition to a slight MP boost. The Bracer of the Guardian (Bracer) sacrifices just 10 HP from Pyra for much more DEF and MP.
The Chancellor’s Cranium synergizes well with the Ninja. It provides significant defenses while ‘encouraging’ getting hit with a short ranged, DPS-boosting proc. As Ninjas are short ranged classes that often take damage, this is a great ring from Chancellor Dammah.
The Forgotten Crown and Chrysalis of Eternity are some of the most coveted rings around, with a decent HP boost and a massive DPS boost. The Chrysalis is a direct upgrade, and requires you to beat the hardmode variant of The Shatters.
The Ninja is a swift and lethal class. His power rivals that of the Wizard, and becomes superior against high defense enemies. Skilled players can take full advantage of the Ninja’s speed and power. The speed boost he possesses can be activated at will, giving him a rushing flexibility exclusive to the class. The stars also allow Ninja to strike enemies well beyond the range of any weapon.
His weaknesses mainly lie with the Katana, a short range weapon that ties the Ninja’s raw damage output down. The speed also takes quite a bit of time to adjust to, especially when considering how frail the class is. At least Katanas can shoot further than swords, and Ninjas are still quite a strong class (their star contributes towards DPS).
Like any melee class, a freshly leveled Ninja might struggle to farm godlands or complete events compared to non-melee classes, largely due to the short range of katana. The Star helps with getting soulbound, but isn’t effective for dealing with bosses.
Ninjas are a fast class; their ability to rush quickly and dish enemy-piercing damage makes them excel on the easier end of dungeons. In many dungeons, the whole group can teleport to you, saving everybody time. With the highest sustained speed in the game, Ninjas are also useful at a unique role: closing realms. While Tricksters with good Magic Heal might be faster, Ninjas are a close second, while the speed is easier to handle than the teleport.
Ninjas remain a frail-yet-powerful class in dungeons where rushing is not important. They can also provide useful debuffs with the Midnight Star’s paralysis, and more dubiously, the Spider Shuriken’s slow.
The Ninja is a very effective class if you want to kill things quickly and have an itchy trigger finger on your ability key. If you want a powerful piercing melee class that can also rush dungeons quickly, and you can manage the lack of armor or healing abilities, then the Ninja is for you.
