Just curious how valuable

I want to think he will be since I caught a 100% Gastly that became one during the Halloween event. However the 1400 candies that I amassed during that event leads me to believe most everyone picked up a Gengar with the moveset they wanted then.

Plus if I'm not mistaken for his uses isn't Sludge bomb more desirable in terms of legacy sets?

According to pogomoves this is the best pokemon to attack now. Shadow claw is a beast, one of my greatest regrets is that I never managed to get a good SC gengar on the past, of 8 I evolved 7 got sucker punch, the only one with shadow claw have only 71% and have sludge bomb, but I still think about powering him up.

I have like atleast 2 84% IV Shadow Claw - Shadow Ball Gengars knockin about.

Kinda disappointed I wasn't able to get a better IV with this moveset...but I evolved so many 91 - 93% ones that just all kept getting sucker punch over and over.

At the time all i wanted was shadow claw sludge bomb but sucker punch haunted me

I suspect when/if trading comes out it will be worth one mon that you would like but don't yet have in your collection.

Hard to tell w/o IVs but for this I'd trade you something with equal usefulness and level. Not sure what exactly

As a collector I would like to have your gengar so yes I think it has value especially if it's 100% IV.