Gengar- is it worth the investment to power up a second Gengar?

Gengar should hit the mews, lugia and celebi very hard, but if they have psychic moves gengar wouldn't survive much hits. T-tar is the best counter for those for sure, but maybe a sludge bomb one hits celebi harder than any othe mon in the game.

Yeah powering it up to 30 would certainly aid in soloing gengar and alakazam raids;

I think even though SBall does make gengar vulnerable for a longer period than sludge bomb, shadow ball is great vs alakazam and necessary vs gengar because gengar double resists sludge bomb :/ for that reason, I would leave shadow ball as is and save the Tm for another pokemon

I have both and can attest