Ninja

Ninja is a perk in Fallout 3, Fallout: New Vegas and Fallout 4.

Effects
When attacking, you gain a +15% critical chance on all Melee and Unarmed attacks. Also, Sneak attack criticals do 25% more damage than normal.

Bugs

 * In Fallout 3, the extra 15% critical chance does not work without the help of the unofficial Fallout 3 patch.
 * In Fallout: New Vegas Ninja multiplies your critical chance by 1.15 instead of adding a flat 15%, unlike all other perks/traits that modify critical chance. For example, a character with a critical hit chance of even 25% would have it be increased to only 28.5% rather than to 40% as it should. (25% * 1.15 = 28.75% vs 25% + 15% = 40%)
 * The bonus to the actual sneak attack damage multiplier on silenced weapons provided by this perk is known to behave erratically when interacting with Cloak & Dagger and Mister Sandman. There does seem to be a bug with the calculations with all three perks active, depending on the order in which they were granted, as follows:

Sandman 3, Cloak, Ninja 3 = 6.3x Sandman 3, Ninja 1, Cloak, Ninja 3 = 5.9x Sandman 3, Ninja 2, Cloak, Ninja 3 = 5.9x Sandman 3, Ninja 3, Cloak = 5.9x Ninja 3, Cloak, Sandman 3 = 6.3x Ninja 3, Sandman 3, Cloak = 6.3x Cloak, Sandman 3, Ninja 3 = 6.3x Cloak, Ninja 3, Sandman 3 = 5.4x (!)

Further testing needed, but right now the only solution appears to be selecting/receiving these perks in the "correct" order.

Ninja Ниндзя Ninja