I just looked at the Pokéjungle leaks. Never mind the fact that one of the alleged Pokémon is called TWINK APE, which would never get past a censor, there's no way someone could get their hands on a demo this early. Also, a dolphin Pokémon? Come on, we all know that Game Freak is never gonna give us that. I'm calling fake lol
Not that I think that, that dex rumor is real, however that being said in regards to the idea that Gamefreak would never give us a Dolphin pokemon, I think it's important to point out that not that long ago some people said the same thing about the idea of a Chimera pokemon or a Koala pokemon and yet in gen 7 we got both, so while this dex rumor is probably fake, I don't think it's safe to say that Gamefreak would never give us a Dolphin pokemon because as long as pokemon keep going and we keep getting new generations of pokemon there is always going to be a chance that we will wind up eventually getting a Dolphin pokemon.
Plus I think it should be pointed out that before gens 6 & 7 that we would never get some of the stuff that we did wind up getting in gen 6 & 7.