Oh, pokepark2. Memories.
I usually just choose pikachu and use an iron tail spam.
I have used snivy's leaf storm like 100 times in a row on round 2 for ferrothorn or someone that resists it and I ended up to knock it out.
For oshawott I get a good distance away and use razor shell. Water gun is also an option if you can't hit with razor shell.
For tepig I enjoy spamming the move where you charge into the opponent. They usually get knocked down and then they try to attack, I would dodge by hitting the -> or <- button and then proceed to use the process over and over again.
As for partners, it seems as if landorus/golurk could help. It always deals a good amount of damage to any opponent. A dragon type Pokemon would work good along with a ground type attacker, as the grounds take out the steels that the dragons can't defeat otherwise.