Bloodthirst
ArmOff
Reaver blood drinks what it spills.
Rolls between 1% and 3%, scaling with the gear score of the item carrying it.
Forge mods that grant it
Spending one of these puts the perk on your gear instead of waiting for a roll.
Rolls on
ArmourCape
A drop or a craft of these types can roll this perk into one of its slots.