Legendary weapon effects are bonuses obtained by defeating certain Legendary enemies.

Weapon	How to unlock
Assassin's	Deal 50% increased damage against humans.
Automatic	Automatic fire mode.
Berserker's	Deal increased damage depending upon your damage resistance.
Bloodied	Deal increased damage depending upon your health.
Cavalier's	Take 15% decreased damage while blocking or sprinting.
Crippling	Deal 50% more limb damage.
Enraging	Your targets frenzy with critical hits.
Explosive	Your bullets to explode on impact dealing 15 area of effect damage.
Exterminator's	Deal 50% increased damage against Mirelurks and bugs.
Freezing	Deal +10 cryo-damage and freeze targets with critical hits.
Furious	Deal increased damage with each consecutive hit on the same target.
Ghoul Slayer's	Deal 50% increased damage against Ghouls.
Hunter's	Deal 50% increased damage against animals.
Incendiary	Set targets on fire for +15 damage.
Instigating	Deal double damage to full health targets.
Irradiated	Deal +50 radiation damage.
Junkie's	Deal increased damage depending upon the withdrawal effects.
Kneecapper	20% chance to cripple targets' legs.
Lucky Weapon	Deal double damage with critical shots with critical meters refilling 15% faster.
Medic's	Heals targets instead of dealing damage to them.
Mutant Slayer's	Deal 50% increased damage against Super Mutants.
Never Ending	Unlimited ammo capacity.
Nimble	75% faster movement speed while ADS.
Nocturnal	Deal increased damage at night and decreased damage during the day.
Penetrating	Negate 30% of the target's damage resistance and energy resistance.
Plasma Infused	Turn enemies into goo and add +10 points of energy damage.
Poisoner's	Poison targets for 10 seconds.
Powerful	+25 extra damage.
Quickdraw	Decrease Action Points cost by 25%.
Rapid	25% increased rate-of-fire and 15% increased reload speed.
Relentless	Refill Action Points with critical hits.
Sentinel's	15% decreased damage while static.
Staggering	Stagger enemies with each hit.
Stalker's	When not in combat, increases VATS accuracy at the cost of increased Action Points.
Troubleshooter's	Deal 50% increased damage against robots.
Two Shot	Shoot additional projectiles.
VATS Enhanced	Increases VATS hit chances, decreases Action Points cost by 25% and 40%.
Violent	Deal 25% damage and limb damage with increasing recoil.
Wounding	Bleed target for +25 additional damage.