Blue has all different types but i beat him with infernape and palkia which i traded from my Pokemon Pearl
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you will need a good level pokemon but your types can be either water,fire or ground. and fight The best pokemon against steel type is fire type pokemon......train your fire type pokemon to high level before you fight with the gym ....
the best Pokemon to use against electric Pokemon is ground/rock Pokemon.
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.
Ground types are best against electric types.
Rayquaza and deoxys are the best ... or at least for me....