Worth using CTM on Gengar?

I think you could try and get Shadow Ball. Especially on that 100% one. Fingers crossed you will get desirable move on the first try.

I don't think there will better ghost type charge attack better than Shadow Ball that Gengar can learn naturally.

Try a couple first!

What are you actually using Gengar for? As a glass counter to Mewto? I have a Hex/SB Gengar powered up a little and don't really use it. Always try to find a reason to power up my own SC/SB one, but until there is a clear use I will hesitate investing.

Yeah, both are worth getting Shadow Ball on. Before raids there wasn't really a reason to use Gengar, because it's so squishy but with raids being a thing, and with specialists being more valuable, and Gengar being the best Ghost-type specialist, it would make sense to get the best moveset available while you can.

Sludge Bomb is comparable to Shadow Ball in a neutral setting, but you're probably not going to use a Gengar in a neutral setting in the first place. When you compare a super effective Shadow Ball's damage to a neutral Sludge Bomb, there's a pretty big difference.

You have so many charge TMs, should moves get changed again and Shadow Ball is still the best move but becomes legacy, you're going to be kicking yourself when you have 30+ TMs in your bag that are not doing anything.

I was sort of in a similar situation with Gengar, I had around 1500 candies from last Halloween and always forgot to evolve into some Gengars, at the time they weren't very useful, and I don't have a single Shadow Claw Gengar because of it.

The 98% SC I would do, since it’s obviously the best Gengar you can get. Otherwise I think it’s better to raid a 15 att H/ShB to power if you need an extra Gengar attacker.

In my opinion, gengar is only worth having if it has shadow ball. Glad to hear you got it relatively quickly.