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).

With the release of Pokémon Omega Ruby and Alpha Sapphire in 2014 Hoenn Region received a complete overhaul with familiar, but improved and expanded storyline, new battle mechanics, gameplay improvements and more and more. Some people theorized that Delta Emerald will be released alongside Omega Ruby and Alpha Sapphire, but of course, it never happened. We've never received a full Hoenn experience in one package. Omega Ruby provided us an expanded look on Team Magma and Groudon, Alpha Sapphire did the same for Team Aqua and Kyogre, and neither of them had the Battle Frontier, which is an Emerald-only feature. Everything is just scattered between different games and we do not have all-in-one version.
That's what I was aiming for when creating this hack. I wanted to bring everything that ORAS improved on into one, complete Hoenn game.
New character designs and new dialogues from ORAS, updated movesets and abilities, Gen 4+ evolutions, Megas and many more!