“The Slayer walks the earth! With a successful Luck roll, all of your hits in hand-to-hand combat are upgraded to critical hits - causing destruction and mayhem.”
Despite the in-game description, Slayer does not need a Luck roll; all hand-to-hand attacks are upgraded to critical hits.
Fallout: New Vegas
The perk increases the speed of all melee and unarmed attacks by 30%.
When completely bare-handed (no weapon equipped), swings will still be at a normal speed and unaffected by this perk.
This perk does not affect Action Point costs. However, the increased speed does make V.A.T.S. attacks execute faster, thus reducing the amount of time that the Courier is "locked" in V.A.T.S. sequences where they are left vulnerable.
The benefit of this perk can be utilized even more with the consumption of rushing water, offering a combination of +80% Melee/Unarmed attack speed.
Fallout: Brotherhood of Steel
Each level of this skill increases your Critical Chance for +5% (up to a maximum +25) when attacking a target.