>>54735674Quilava, Flaaffy, Quagsire, and Noctowl should form your core by the time you enter Pyrite Town’s Colosseum(TM). Skiploom and Furret both have different styles of support roles (debuffing enemies and buffing allies), while Dunsparce has excellent role-compression with Glare and Yawn (Yawn one opponent, then Glare the other on the next turn to completely shut down the enemy team).
Sudowoodo and Hitmontop gained immediately after Pyrite Town’s arc share the same bruiser role but with different styles—spreading damage with Rock Slide, or focusing down individual targets with Focus Energy -> Triple Kick.
After that, you can start swapping mons around at your leisure. Maybe you decide to swap Quagsire out for Piloswine or Suicune, or pair up Forretress’s Spikes with Granbull’s Roar (not that you realistically would).
Due to the funny and well-documented quirk in Colosseum’s AI, Misdreavus fulfills a role as an evasion tank when put in the front of the party due to the AI prioritizing that slot even when a move will be NVE or completely nullified, but tying Shadow Ball to Misdreavus’s whopping 60 Attack stat is… wasted potential.