http://www.pcgamer.com/destiny-2s-prometheus-lens-exotic-is-completely-broken-and-a-menace-in-pvp/

Destiny 2's first expansion, Curse of Osiris, is now live, bringing a shot of fun campaign content and a much-needed patch. Among other improvements and fixes, the coinciding patch included nerfs to problem PvP weapons like the Uriel's Gift auto rifle and Last Hope sidearm. Yay! Or not. Little did we know, the expansion also added the most overpowered weapon in the history of Destiny PvP: the Prometheus Lens, a new exotic trace rifle. 

A sister weapon to Coldheart, the Prometheus Lens also fires a steady laser beam. But instead of building up damage like Coldheart, which is actually pretty weak in PvP, it generates a heat field around the user that expands as Prometheus is fired. Getting kills with it also refills the magazine, but the key point is that the beam's damage is constant, because it is fucking nuts.