Pokemon Vega English translation
ポケモン ベガ · Pocket Monsters Vega
Dr. Akimbo's English translation of Pokemon Vega, a notoriously difficult Japanese Pokémon hack with a new region, new monsters and a custom soundtrack.
What it is
Pokemon Vega is not an official game but a Japanese fan hack, and one of the best regarded in its series. It takes you to a new region with original maps and sprites, a full custom soundtrack, new moves, and a roster where most of the catchable monsters are fan-made designs. It sits between Altair/Sirius and Procyon/Deneb in the story.
Why people warn you about it
The difficulty is the main talking point: gym leaders are set well above the level of your team, wild monsters lag behind so grinding helps little, and the leaders' AI plays much smarter than normal trainers. A Vs. Seeker is included so you can rematch trainers for experience.
What's translated
Dr. Akimbo's patch from April 2019 brings the hack's text into English, so the story and the new monsters' details can be followed without Japanese.
Playing it
The patch is applied to your own copy of the game following the instructions in the translator's release thread linked here.