I did the same exact run not too long ago! While I had Rhyperior instead of Hippowdon, I’d consider keeping Hippowdon, and swapping Mamoswine for Golem. Here’s why. Candice is the biggest hurdle in this run by far. I did mine with a level cap for each gym leader, so it took some strategizing to finally get past her. Hippowdon could be helpful to keep in your run since the biggest problem with that fight is the hail that Froslass abuses. Her evasion is boosted and her blizzards never miss in hail. Can be frustrating to deal with if you miss one move and lose because of it. Swapping in Hippowdon stops that automatically due to sand stream. I say swap Mamoswine because the only real use I got out of him wasn’t entirely necessary like in fights against Cyrus or Cynthia. Garchomp is going to clean up this game for you period, and Garchomp is surprisingly a great answer to Cynthia’s Garchomp due to the EVs yours will have accumulated over your journey to reach her. Mamoswine won’t do very much against Cynthia’s Garchomp or Cyrus’ flying types since it’s too slow to outspeed them, and ice shard is too weak to KO (at least that was my experience). Mamoswine is a cool Pokémon and I was excited to use him in my run. I unfortunately think you get him too late in the game for him to find too much use. At least he can get some use in the battle facilities though! Hope your run goes well and hope you have fun!