The goal of my other rom-hack, Pokémon Delta Emerald, was to create a game that could be played as a companion to Pokémon Mega Blue, which is a rather modest project. You can complete the entire Pokédex by only playing these two hacks because, when combined, they offer access to all of the Pokémon in the game’s database.

It’s basically the same as FireRed and LeafGreen, but with updated mechanics, Alola Forms, and Mega Evolutions (although the latter two are more prevalent in the post-game). The storyline remains the same, with the exception of the addition of Ariana and Archer.

Features

A vast majority of features are provided by an old version of Leon and UltimaSoul’s FireRed Base, it’s better you look them up in the rombase’s thread.
I’ll just list the most notable ones:
Fairy-type
Gen 4-7 Moves and Abilities
Mega Evolutions
Physical/Special Split
Expanded bag capable of holding every item
Day and Night System
Game is fully decapitalized
B2W2 Repel System
Poison survival at 1 HP
Emerald-style Pickup ability
Eggs hatch at level 1
Running indoors
Pokémon stats updated to the standards of Gen 7
Over 25 new overworld sprites by Kalarie
Game Freak presents fix
Nature-colored stats
PokéMart items depend on your badge count
Ultimate Move Tutor is infinite use for Gen 1-3 starters
Roaming Legends IV Fix
Infinite TMs
Deletable HMs
Disabled badge stat boosts
Disabled LR help menu
Disabled Flashbacks (“Previously on your quest”)

Features separate from the rombase:

Updated Pokémon sprites and cries
Gen 4+ Evolutions of Gen 1-3 Pokémon with their respective Evolution methods and items
National Dex is expanded to include new Pokémon
All 150 Kanto Dex Pokémon (except Mew) are catchable without trading or events
All Trade evolutions now evolve also by just holding their evolution item and leveling up
(Machoke, Kadabra, Graveler and Haunter need a new Link Cable to evolve)
You can get all evolution items from Lady Selphy at Resort Gorgeous
All non-Kanto Dex Pokémon that are available in vanilla FireRed and LeafGreen are also catchable (except Deoxys), as well as all three Johto starters and Celebi
All three Legendary Beasts are obtainable, the next one begins to roam when you enter a Pokémon Center after catching the current one
Alola Forms can be found as wild encounters on Sevii Islands
Pikachu, Exeggcute and Cubone will evolve into their regular evolutions in Kanto and into their Alolan evolutions on Sevii Islands
Pokémon gain experience after capture
Infinite Move Tutors
Proper item fanfares
ipatix HQ Sound Mixer
Archer and Ariana are also included in the main plot, not only the post-game
Koga’s and Blaine’s teams are tweaked to include more diverse Pokémon, Sabrina’s Venomoth is replaced with Hypno
Gym Leader rematches become available after giving Sapphire to Celio
And that’s all of the features, if I didn’t forgot something :’)