Found in Valley of Drakes, near the flood gate doors to New Londo Ruins. While looking at the flood gate (from the Valley of Drakes side), there is a ladder to the right. Climb it and locate the ring at the top.
With your health at 20% or less, the ring will grant 50% more damage to weapons and spells. This is most useful with ranged weapons. Wearing the Ring of Fog at the same time can make you into a sniper ninja that the enemies simply never see.
Almost completely useless for online games as the damage bonus will not kick in until you are on your last legs.
The Blue Tearstone Ring compliments this ring, with a 50% boost to defence at 20% health.
Capra Demon. Not a melee enemy to take on with only 20% HP. Try a ranged attack instead.
Grants 50% increase to damage by weapons and spells when you have 20% or less health.
Can be stacked with other damage increasing items.