ok this sounds soooo stupid but i cant get past the FRST GYM BATTLE it suks and i dont hav a charger to charge my gamboy plz help and reply!!!!!!!!!

Evolve a Caterpie to a Butterfree and use Confusion. One of the best methods.

oh thanks i hav 2 metapods thats sooo awesome thanks a bunch!

Another way would be to get a Mankey and train until level 9 I think and use Low Kick

Epic levelling and a little luck works. Oddly enough I trounced Brock with nothing but a level 13 or so Charmander behind the wheel on my first try.

you cant get charmander till cerulean city.....so your ether lying or you have traded with your self to give your self charmander or your talkin about red or blue which shouldnt be in this forum because its about yellow but in anycase i dont like using bug pok'es but there the best way to go on brock at the begining

Not particularly.

Mankey learns Low Kick somewhat early on, which is even more effective than Butterfree's Confusion.

Nidoran♂ and Nidoran♀ can also be useful with their Double Kick.

I do believe Double Kick, like Karate Chop, was a normal type in RBY, wasn't it?

No it was a fighting type, granted a weak one but fighting none the less.

Hm. My mistake, seems you're right. I should mention that Mankey learns Low Kick three levels before either Nidoran (9 as opposed to 12), though, not to mention that, because of its sheer size and weight, it's extremely effective against that troublesome Onix.

Size and weight make no differance in Pokemon.

... they make every difference. Obviously you don't know what Low Kick does. XD

The heavier the victim, the greater the damage. It will do much greater damage to Onix than to Geodude, mind you it will be considerably effective against both.

I think training a Caterpie into Butterfree is the fastest way to defeat Brock as they grow fast which means they level up fast.

quote Xelrog T Apocalypse

... they make every difference. Obviously you don't know what Low Kick does. XD

The heavier the victim, the greater the damage. It will do much greater damage to Onix than to Geodude, mind you it will be considerably effective against both.

How ironic, even after having been corrected on another attack earlier. For your information, Low Kick is simply a standard attack with a chance to flinch the target in Generation I. The change in the way it deals damage was only made from Generation III and onwards. And Pokemon Yellow is Generation I.

If you do not know how things work, then at least check them up in bulbapedia, instead of just posting erroneous stuff with such confidence.