I haven't played Pokemon since the Silve/Gold generation, so I don't know the specifics of dual battles, environmental effects, or other features introduced in later iterations.
1: Furret/Eevee
2: Dewgong
3: Skarmory
4: Sableye
5: Heracross
6: Torterra
1: Furret/Eevee
2: Dewgong
3: Skarmory
4: Sableye
5: Heracross
6: Torterra