Gengar's Moveset in Pokemon GO has just received a new addition in the form of Shadow Punch. Haunters that were evolved into Gengars during, or less than two hours after, Sunday's community day gained the exclusive move Shadow Punch. Shadow punch is a charge move with a base power of 40 and an energy cost of 33. This gives Gengar a new total of seven possible charge moves.
Gengar Moveset Pokemon GO: What's the Best Moveset for Gengar?
If you're looking for pure DPS on your Gengar build that's going to be a no. Shadow Ball is still going to be your best bet for dealing out as much damage as possible during raids. What Shadow Punch will do, is open up some interesting options in PVP. Shadow Punch charges much faster than Shadow Ball, letting Gengar get off one last split second attack before it goes down in matchups with psychic types it has issues with like Mewtwo, Shadow ball is still a bit more stable overall, however, dealing consistent high damage even when it runs the risk of getting one-shot killed. There is something to be said about Shadow Punch's ability to bait shields but as a glass cannon, Gengar might not get as much utility out of that application.