Just use 'rock smash' on magneton and it'll lose! And make sure you leave vigaroth at full
hp ok?

Eletrics weakness is ground right so... You hit magneton with rock smash it will hurt it
alot follow this guide and you will win it you dont listen you lose hope you understand

Catch a geodude in dewford cave and raise it to lv.16 when it will learn magnitude, which
faints all his pokemon in one hit each.

Restart the game(don't worry). Then choose mudkip. Do not catch any other pokemon. You
will be able to beat all the trainers with it. For the first gym,beat everybody you can
even on the route with the nincadas. Then challenge the gym. Before the third gym beat the
cycling road too. When you reach watson you should have a marshtomp and a powerful one at
that. Marshtomp is water/ground type. Electric attacks do twice the damage on water but
don't affect ground types. Therefore, 2x0=0. Electric attacks wont work on marshtomp. And
since you've beaten all the trainers accesible with it, it should be knowing mud-shot.
Mud-shot is super effective against all his pokemon. Plus if you did everything i told
you, they will faint in one hit of mud-shot. And remember mud-shot not mud-slap.

I would recommend getting a sixth pokemon... Other than that, i can't help.