Red Death is an Exotic Pulse Rifle, notable for high Impact and its strong healing effect. Its namesake talent will heal you to full in under 2 seconds after a kill; it'll also briefly speed up your reload. Considering those benefits, Red Death is all about keeping you in the fight. This makes it a great choice for Guardians with a low Recovery stat.
In the December Exotic Patch, nearly every Exotic weapon was buffed. Red Death was not, and was arguably nerfed. Its previous Impact/ROF was 30/59. This was changed to 26/66 – a faster ROF with lower Impact.
In Patch 1.1.1, the damage for all Pulse Rifles was increased +9.7%. This return Red Death to its former damage numbers, while still maintaining the higher ROF. A net benefit in the long run!
Red Death has very little Lore. The Grimoire card only has a description & a few lines:
Vanguard policy urges Guardians to destroy this weapon on sight. It is a Guardian killer. Only rumors tell of the mad Guardian who fashioned this butcher's tool. But its power is undeniable, and fear is a formidable weapon.
"Vanguard policy urges Guardians to destroy this weapon on sight. It is a Guardian killer."