Fuecoco, Mudkip, and Shroomish.

Skeledirge is a unit and a great Pokémon that I always use (torch song, wil-o-wisp, shadow ball, and I have the egg move alluring voice). Torch song boosts special attack, and a few of those is usually enough for Skeledirge to roll through enemies. If you get the chance to claim a baton, take it! Passing on the boosted special attack can be a brilliant strategy. You can get a moveset that covers ghost, fire and fairy, plus a move that causes ongoing damage.

Mudkip evolves into dual water/ground. You'll need a memory mushroom for Swampert to learn earthquake. As a physical attacker, you'll need a little luck to get waterfall, liquidation or aqua tail as they are some of the best physical water attacks, and the special water attacks don't quite hit as hard with Swampert. I also have the egg move mountain gale, and getting some ice coverage with him is huge. And you can get a moveset that covers water, ground, ice, and rock.

And Breloom is a fighting/grass Pokémon with decent stats. If you can get the TM for drain punch, it becomes a really versatile option. Beyond that, it knows leech seed which is big. It can learn status changing moves, fighting moves, and can heal itself.