The Lental region is close to the Alola region
The Pokémon that can be found there appear to be from all the other regions, but curiously it has some Alolan forms as well, specifically Alolan Raichu, Alolan Vulpix and Alolan Sandslash. Curiously it also has regular Ninetales and Sandshrew and regular Exeggutor as well. Most of the Illumina Pokémon were granted immortal life
Since the main source of Illumina power seems to be Xerneas, all of the Illumina Pokémon had been affected by its power. Although some like Steelix and Wishiwashi may have naturally long lives (Wishwashi's individual members are replaced over the years as new fish are born and others die or are eaten). Professor Mirror is ignorant of predator-prey relationships
It's stated that he doesn't leave the lab often, so it's entirely possible that in his world-view, a group of Mareanie chasing down a Corsola (who has a terrified look on its poor little face) is just a friendly game of tag, after all, if he saw his Pokémon chasing each other in the lab, it probably would be a game of tag...