Merciless

Merciless is a Solar Exotic Fusion Rifle that ramps up against a single target.

Overview

Its intrinsic perk, "Conserve Momentum", makes non-lethal projectile hits charge the weapon faster until you get a kill. The effect persists through weapon switches but resets on reload, so you can soften a target with Merciless and finish with another weapon. Archetype: Fusion Rifle (Energy slot). It also has anti-unstoppable capability and is good against high-health enemies and Solar shields.

Acquisition

• Exotic engrams and extremely rare world drops.
• Xûr occasionally sells it.
• Introduced in Season 1 as a Power weapon; the Forsaken expansion moved it to the Energy slot (Destiny 2 Wiki).

Catalyst

The Destiny 2 Wiki says the catalyst is earned in Heroic or Nightfall Strikes, and increases range and stability while masterworking the weapon. Destinypedia instead lists a "Heal Clip" catalyst perk granting Solar Cure to you and nearby allies after reloading after a final blow; these may reflect different eras, so verify in game.