Pokemon that we can't capture in the game, just trade from another one, are listed in the national pokedex right? Not on the native.
There is any other way to get him without trade from another game? And also, before the national pokedex?
It is possible to get Goodra's evolution line in S&M without trade. You can catch Goomy through SOS during rain at Route 17 and Lush Jungle. You can catch Goomy's evolution, Sliggoo, through the same method on Exeggutor Island. That is why Goodra's evolution line is in the Alola Pokedex.
Goomy and Sliggoo