"All of creation cares not whether you live or die."
Mercy is one of Strife's two revolvers, the other being Redemption. The achievement/trophy "An Old Friend" is unlocked upon gaining it. Once you kill the Griever, War walks in on Ulthane pounding away on his anvil with a hammer at which point he gives Mercy to War. With it, War questions the blacksmith while Mercy is aimed at his head. Mercy generates its own supply of ammunition, so it doesn't have to be reloaded. Unlike Redemption, Mercy has an unlimited "clip", which means War can keep pulling the trigger forever without ever coming up empty. The drawback is that each individual bullet does significantly less damage than the ones fired by Redemption. This weapon is necessary for taking down Ashworms, including the Stygian, one of the Chosen.
Although Strife is indeed described as wielding a revolver named Mercy, it is a weapon gained by War in Darksiders from Ulthane. It is unclear as to how it came into his possession, but from his dialogue, it can be surmised that he admires its craftsmanship despite the fact it is too 'dainty' for him to use. As with the Crossblade, the damage Mercy does is greatly increased once War has obtained the Legendary Enhancement known as Strife's Offering.
The gun's counterpart, Redemption, is gained in Darksiders II by Death. It is unknown how or why Strife's guns were separated from their owner and each other.
While at the end of Darksiders III it was revealed that Jones was Strife in disguise, it's unknown as to what became of him after Fury left with the remaining human survivors through the portal that was made by Ulthane.
Mercy has the following upgrades that can be purchased from Vulgrim:
- Impact Rounds, 4000 Souls - Augments the amount of damage done by Mercy, and increases its rate of fire.