>>48084909These are not fossils, they are varieties or subspecies that disappeared due to the cessation of their breeding or the loss of their environment.
The most realistic thing would be to bring them based on breeding as is being done in real life with cases such as the Aurochs, the Tarpan, or ancient dog breeds. The genes are there, it is a matter of genetic selection work to bring them back.
Now how can this be replicated in the game? You could obtain an H.Growlithe through selective breeding, for example by breeding a male Lycanroc with a female Arcanine and the resulting offspring (an apparently normal Growlithe) by reproducing it with a Pyroar, the result of this chain gives you a H.Growlithe .
It seems to me an original way to have "new" pokemon, but if it is too complicated for people to understand it, simply solve it with an NPC giving it to you and when they ask him where he got it from, he answers "That's a mystery" or only use a "magic" incense.
