Hello why not implement the mirage island in HOENN, I think adding it will do a plus in this region.
For example, take the basic principle where the old man in Pacifidlog Town selects 1 pokemon among all the pokedex each day and makes the mirage island appear,
To make the island appear, we will therefore have as a condition to speak to the person with the right pokemon in our team.
So it's up to us to guess among all the Pokedex
Obviously, each PokeMMO player will not have the same Pokemon otherwise it will be too easy.
You can add very rare pokemons to the island that have rare items or even rare berries ...