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Geodude is an incredible Pokemon for GSC. I'm not talking about HGSS because Levitate exists in that game. I mean old school GSC is absolutely destroyed by Geodude. You can first encounter Geodude on the path on the other side of the gate just a little ways away from New Bark Town. You'll probably encounter it at level 2 or 3 here.
Raising it might seem intimidating at first. Until you realize that its Rock-typing makes it resistant to every attack the Wild Pokemon on the route have at their disposal. This makes grinding very easy, as there is virtually no risk of your newly acquired Geodude fainting. But it's not just the Wild Pokemon between New Bark and Cherrygrove. It's the Trainers too. None of the Pokemon owned by any of the Trainers between Cherrygrove and Violet City are capable of dealing normal damage to Geodude. This means if you can put it at the front of your party and soak up massive amounts of experience before you hit Falkner. For added benefit, go ahead and do Sprout Tower before the gym. You'll be surprised at how much of a non-threat the many Bellsprout inside are.
From level 11 to 16, Geodude learns Rock Slide and Magnitude. This is more than enough to sweep through Falkner, Bugsy, Whitney, and Morty. Levitate doesn't exist in Gen 2 so Magnitude will hit all of Morty's Pokemon for Super Effective damage. But you don't even need it, because Rock Slide is strong enough as is and if Geodude has been your consistent front man, it should probably be a Graveler by the time you get to Morty too.
But the fun doesn't stop there. You technically don't have to fight Chuck before you fight Jasmine. If you choose to get the medicine, go back to Olivine, return Jasmine to her Gym and then fight her, Geodude/Graveler will make short work of her entire team with Magnitude. Which means Geodude can, at minimum, sweep five gyms in a row, four out of those five with Super Effective damage.
