Any value?

Dewgong is a fairly rare Pokémon, so keep it.

Zero value unless prestige becomes a thing again.

There's no value for any trading of any type in PoGo. It's a good collector's piece, though.

One of the stupid things about this game is that true collecting is pretty much out of the question with the 1000 pokemon limit. If there was no limit people would be keeping all sorts of weird pokemon, keeping all different movesets etc and stuff like pokemon with legacy movesets would indeed be valuable. But with the hard limit of 1000 pokemon all of this pretty much goes out of the window. Too bad.

I would trade with you ;). I could even give a legendary 93, or some other 98 mon, not that would be usefull, i just like that pokemon and like me there are others. There is also this complaining about the max slot for pokemon, i really don't think 1000 is a bad number, there is no meaning in keep thouns of mon that u not even remember you have.