UNITS:
Jolteon - The biggest reason to wait until after Erika to evolve it is so you can get Bite at level 30 as an EeveE. Also Game Corner means that I have an essentially limitless amount of Thunderbolts and Ice Beams, so get used to seeing the move.
Pinsir - The unexpected hero of this segment, since it can 1 shot this particular version of Giovanni's Kangaskhan thanks to the drastically increased level cap. His Pokémon have perfect IVs for his 1st and 2nd fights, believe it or not.
STRATEGY:
It's Jolteon for the 1st 2 grunts, Zam for the last 2, and Pinsir for the Giovanni fight.
The Rival fight is cleared in 5 turns.
STRATEGY:
Hit the correct attacking move with Zam and you win. Congrats.