Pokemon Trainer Guzma
Guzma's definitely been training his Pokemon.
Golisopod you should be all too familiar with. As always, it has First Impression, which goes first but only on the first turn it appears. Therefore, avoid leading with Pokemon weak to Bug-types.
Masquerain isn't particularly notable, although it does have plenty of coverage moves, including Bug, Flying, Ice and Grass. Electric-types are your safest bet. Only go with Rock-types if they're fast.
Scizor can be tricky with powerful STAB moves and Bullet Punch to take out weakened foes. That said, it takes huge damage from Fire-types moves, so use one of them if you can.
Ariados is another mainstay that can now use Toxic Thread to poison and reduce Speed and Cross Poison as a powerful Poison-type STAB. Try not to let it grab a KO or it can sharpen its Attack with Fell Stinger.
Finally, Pinsir has Guillotine to try and score a OHKO, Stone Edge to punish Fire and Flying-types and Storm Throw to punish Rock-types. That leaves few Pokemon as safe choices. Perhaps go with Ghost-types.
Wipe the floor with Guzma and he'll give you a rare Dawn Stone, which evolves female Snorunt into Froslass, among others.
A Final Lesson
Thought you learned everything there was at the Trainer's School? Not quite... Whenever you're in the neighbourhood, go up to the top floor of the Trainer's School building, then make way along the corridor to the west. Standing in front of the door is a stubborn Pokemon trainer.
Black Belt Duane
Primeape is a pretty straightforward powerhouse. Lucario is somewhat trickier since it's part Steel. It won't be weak to Flying, Fairy or Psychic-types, but gains a weakness to Fire, Fighting and Ground-types.
Defeat Duane and he'll step aside, allowing you to proceed through the door. On the other side, you'll meet another trainer who's all too eager to challenge you.
All of Asuka's Pokemon have Intimidate, which lowers Attack. Therefore, it's a good idea to fight back with special attackers. Alternatively, stat gains and drops can be eliminated by switching Pokemon.
Hold your own against Asuka's intimidation and you'll be rewarded with a King's Rock that enables all attacks to cause flinch, while also being an evolutionary item for Slowpoke and Poliwhirl.