1635 | - Pokemon Fire Red -u--squirrels-.gba Rom-

The reason lies in the stability of the "1.0" version of the game. Later prints of Pokémon FireRed fixed minor glitches, but the "squirrels" dump (often correlated with the Rev 0 or Rev 1 initial run) became the "Universal Cartridge." It became the standard for the Pokémon Randomizer, a tool that shuffles the encounters in the game, allowing players to catch Charizards in Route 1 or Mewtwos in Viridian Forest.

It looks like you’re referencing a specific ROM filename: 1635 - Pokemon Fire Red -u--squirrels-.gba Rom-

Downloading ROMs of games you do not physically own is considered piracy. To stay legal, you should dump the ROM yourself from your own Pokémon FireRed cartridge. The reason lies in the stability of the "1