v1.0 (revision 0) release of the game. Later official retail versions (v1.1) moved internal data around, making them incompatible with many fan-made mods. Why is it so popular? Most major Pokémon ROM hacks are built specifically on top of this file because its data addresses are consistent and well-documented. You’ll often see it required for: Pokémon Unbound : One of the most advanced fan games that requires this exact base to patch correctly. Pokémon Radical Red : A notoriously difficult "difficulty hack" that uses the Squirrels ROM as its primary foundation. Pokémon Clover
Why would a fan-game pick specifically? There's no obvious Pokémon link, but two strong historical coincidences stand out: 1636 pokemon red squirrels
