Pokémon Emerald Plus and Double Plus are two patches designed to allow you to enjoy the base game with modern QOL improvements.
PE Plus brings in changes like faster battles and all improvement from the Battle Engine Upgrade, the B/W Repel system, colored natures in the status screen, the ability to evolve trade evolution Pokémon without trading, the ability to forget HM moves like any other move, etc.
PE Double Plus brings in even more radical changes like Fairy Type, Gen VII battle mechanics, the ability to switch between the Acro and Mach bike with the R button, infinite TM usage, toggleable exp. share, etc.
No changes were made to the story or Pokémon, so the game should feel familiar, but more accessible and modern than ever. Please read the readme for a full list of changes.
Evolution chart:
Poliwhirl - Politoed (Level up while holding King's Rock)
Kadabra - Alakazam (Level 37)
Graveler - Golem (Level 37)
Machoke - Machamp (Level 37)
Slowpoke - Slowking (Use a Water Stone)
Haunter - Gengar (Level 37)
Onix - Steelix (Level up while holding a Metal Coat)
Seadra - Kingdra (Level up while holding Dragon Scale)
Scyther - Scizor (Level up while holding Metal Coat)
Porygon - Porygon2 (Level up while holding Up Grade)
Clamperl - Huntail (Level up while holding DeepSeaTooth)
Clamper - Gorebyss (Level up while holding DeepSeaScale)
Note: The readme has been updated to include more accurate credits)
Database match: Pokemon - Emerald Version (USA, Europe)
Database: No-Intro: Game Boy Advance (v. 20210227-023848)
File/ROM SHA-1: F3AE088181BF583E55DAF962A92BB46F4F1D07B7
File/ROM CRC32: 1F1C08FB