FIRE RED EXPANDED is a mid-effort hack (patch) of Fire Red that adds/replaces encounters in routes, changes up some trainer fights and makes important battles more fun and overall tougher. Plus, Bulbasaur and Squirtle are instead replaced with Treecko and Totodile, and Charmander is still there; did that just so it's a different experience.
NOTE: When patching, make sure to use the Squirrels version of Fire Red to play the hack. I have no idea what would happen if you used a regular Fire Red ROM, the game might as well just break, i actually have no idea
Anyway uhh have Fun lol