Bertha

General Info - Bertha uses a lot of Ground types, with the exception of Sudowoodo which is only Rock. If you have a fast Grass type, then this should be the easiest battle out of the Elite Four. The Grass type actually doesn't need to be all that fast, as most of Bertha's Pokemon are pretty slow, it just has to out run the ones that carry Ice type attacks, such as Wishcash. Of course, Ground has many other weaknesses that Bertha is just asking for you to exploit.

Lv55 (Water/Ground) - Quagsire is Water and Ground, giving it a 4x weakness to Grass but neutralizing Ground's weakness to Water and Ice. So attack with Grass types, if not then attack with the hardest hitting neutral attacks you have. Quagsire can have some pretty big defenses. On the first move, Quagsire will most likely use Protect, so you could use that to get a stat boost in quickly.

Lv56 (Rock) - Take your pick of Ground, Grass, Steel, Water, or Fighting type attacks to take down Sudowoodo, who isn't very threatening in any way.

Lv54 (Rock/Ground) - You have delt with many Rock/Ground types throughout your journey, and Golem should not be handled any differently. Water AND Grass attacks do 4x damage, and Ground, Ice, Steel, and Fighting attacks are still super effective. Rock/Ground is pretty much the worst type combo, in my humble opinion.

Lv56 (Water/Ground) - Wishcash is basically the same as Quagsire, but with less defence and slightly stronger attacks.

Lv59 (Ground) - Hippowdon can be extremely annoying if you arn't prepared for it with the proper Water, Grass, or Ice type attacks in your arsenal. Hippowdon has the Sandstream ability which damages every Pokemon in battle that isn't a Rock, Ground, or Steel type. But that shouldn't be too much of problem, especially if you are using a Pokemon with the Sand Veil ability which raises that Poke's evasion in Sandstorms. So basically, attack with your hardest hitting Grass, Water, or Ice type attacks and hope Hippowdon goes down quickly.