i have used mankey or butterfree

you cant use a pikachu because rock pokemon are immune to electric attacks.what i did was i got a caterpie and evolved it to a butterfree.caterpie will evolve to butterfree at level 10.anyway by then butterfree should have learned confusion (an attack).keep your oher highest pokemon next,other than pikachu.the only way you can fight with pikachu is if you keep on fighting with him in tall grass.keep on doing this until he learns (quick attack).tust me pikachu will learn it some time soon,but i know that he will learn it before he gets to level 13.
even though pikachu is pretty tough when he uses his (quick attack), you might want to put pikachu as your 3rd choice of pokemon in battle.with butterfree what youll want to do is,just keep on using (confusion) and your sure to win.
BUT just in case, make sure you bring backup pokemon.

first you have to catch a caterpi.raise it to level 12 and it will turn into a butterfree.use butterfree to beat brock.

no use a pidgy, it's probably easier, or a pigeotto, since u can't use thunder attacks stick to quick attack

just trade one of your friends for a water or grass pokemon, if not do what hte others said with butterfree.

I used male and female nidoran (ther double kick is super effective)

avoid him or not suit yourself try it i did it avoid him if you defeated him he don't
challange you trust me