Half of my playthrough was just this:
..which is pretty cool, I guess.
And then I won.
Oooh... the suspense...
Hall of Fame!
Yeah, I used Mence. But he evolved after Sidney, and only really helped during the battle with Drake.
And, the whole crew:
Shedinja is a beast. Shedinja took out Gyarados, Wishcash, and Wailord single-handedly.
Numel was fairly useless until I got Earthquake and taught it Flamethrower. It had its moments, though.
Salamence didn't really do anything aside from help with Drake.
Tropius's Magical Leaf was awesome, hitting Wallace's Ludicolo through Double Team. Learning Fly is a great plus, and Body Slam is great for paralyzing.
Slakoth was pretty much useless. Vigoroth was heavily used mid-game, though his usefulness declined slightly towards the end, basically just Yawning things. A 100% accurate sleep move is incredibly useful, though.
Azumarill was great mid-game. It's unfortunate that he got stuck with Strength, Surf, Waterfall, and Dive, though the good type coverage made up for it. Azumarill's Strength and Rollout was very useful.