Is it worth trying to get Shadow Claw Gengar for regionals?

If you're drowning in revives, sure. SC Gengar kicks butt every second until it goes down, but unfortunately, there aren't that many seconds before it goes down. The only relevant time it can take a big hit is against Focus Blast Mewtwo, but then it can be a lifesaver if you're short-manning it. It's good against Machamp, but there are better options.

That said, this is a game. If you love it, go for it. Might not be ideal use of resources, but if it makes you happy, who cares?

I have a level 40 SC Gengar and I hate it. It is just too glassy for my liking. I would never go in with a team of Gengars. However, if you like it, and are an expert at dodging, go for it.

I have two maxed (both 14a). I’d trade my spare one (however, the price would be 10 unique shiny species). My end: SC Gengar+9 alolan rattata, you: 10 shiny

If you like using glass cannon yes..
I like it and wont trade 3 my SC Gengar..
But some dont like it
But if that make you happy without too much cost then why not..

I can trade you my level 20 one, if Niantic removes the 100 meters limit.