This weapon fascinates me. The clear objective of it is to have a big opening attack. Who has the best opening that could really make this thing shine once per combat? The immediate choice would be starlit span with true strike and shocking grasp. Follow up with a bow in spirit sheath. A rogue with archer archetype could open with parting shot. A weapon inventor can megaton strike with it. Although, would need to have dual weapon form otherwise you throw your class abilities away on the first attack. What else? Or other thoughts on this sort of weapon/strategy?
Stealthy Investigator. Hide and Devise Strategem until you crit, then launch the shot.
Unexpected Sharpshooter. Accidental Shot has Fortune but is only usable once per day.
I thought about the investigator but then, I'd rather have a fatal gun for that kind of play I think. But with DAS, you can make sure you don't miss if you're in the middle of combat. Unexpected sharpshooter is a good one. Definitely unexpected from this contraption.