Pokémon Mega Blue is a rather small project, aimed to create a counterpart game for my other rom-hack, Pokémon Delta Emerald. Together, they provide a full roster of available Pokémon, so you can fill up the Pokédex playing only these two hacks.
Essentially, it's still the same FireRed and LeafGreen with an unchanged storyline (except for an addition of Ariana and Archer), but updated mechanics, Alola Forms and Mega Evolutions (the latter two are mostly in the post-game, though).