Celestial Nighthawk is an Exotic Hunter Helmet which transforms your Golden Gun into a one-shot cannon with 6x damage. Ultimately, this means you deal twice as much damage in 1/3 the time.
For PVP, Celestial Nighthawk is not recommended. It's overkill on one target and won't lead to more kills.
For PVE, it's worth considering. While you lose the versatility of spreading shots to multiple targets, you gain significant damage while Keyhole grants target penetration. You'll need to patiently line-up shots to make it truly worthwhile. If you have Nighthawk equipped, remember to choose either the Scavenger or Gunslinger's Trance class perk.
- Nighthawk's most interesting use thusfar is to remove Crota's shields in a single shot (on Normal).