I believe you're referring to a ROM hack or fan-made modification of Pokémon FireRed titled “1636 - Pokemon Fire Red Squirrels” (or similar). However, after checking multiple reputable ROM databases, hack repositories (like PokeCommunity, Romhacking.net), and archives of numbered releases (e.g., No-Intro, GoodSets), no official or widely known hack exists under that exact name and number.
Here’s a complete breakdown of what I can verify and what you might be confusing it with:
Despite its janky execution, the sheer volume of content added to a GBA game was unprecedented for its time.
The hack is infamous for its difficulty. The third gym leader (Lt. Surge) replaces his Pikachu with a level 36 Thunder Squirrel that knows Extreme Speed and Nut Bomb. Players who search “1636 Pokemon Fire Red Squirrels” are usually looking for a walkthrough for this specific hack.
Where to find it?
The original download link is dead, but archived versions live on romhacking.net under the ID #1636 (coincidentally). A direct search for that archive ID yields the patch file. 1636 Pokemon Fire Red Squirrels
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If you want, I can:
Strip away the squirrel logo, and you are playing the gold standard of Pokémon remakes. Pokémon FireRed is widely considered one of the best entries in the series for a reason:
The most likely source of the keyword is a cult-classic ROM hack created in 2016 by a Spanish-speaking developer known only as "Mantarraya." The hack’s full title is Pokemon Fire Red: Insurgence of the 1636 Squirrel Army.
If you are playing a vanilla Pokemon Fire Red (unmodified cartridge or official Virtual Console), you will never see squirrels or the number 1636. However, if you are playing a specific ROM hack, follow these steps reported by fans: I believe you're referring to a ROM hack
Disclaimer: This is a fan-made glitch guide for a specific ROM hack, not an official Nintendo feature.