The fifth gym leader Koga uses Poison type pokemon so your best bet is to use Psychic or Ground types against them. A Kadabra(Alakazam would be even better) can easily take care of all of Koga's pokemon.
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beat everyone in silph.co and you can get into the saffron gym
geovanni is the gym leader hes easy to beat if u have water Pokemon
You have to beat Erika, who is the fourth Gym Leader, raises Grass-Type Pokemon, and resides in Celadon City.
He disappears until you beat the Pokemon league again.
You have to beat team aquas leader. His red orb will glow and kyogre will wake up.