Smeargle. Smeargle can easily put Pokémon to sleep with Spore, and with a Focus Sash it guarantees a Spore to effect the opponent. It can even use Recover or Soft-boiled to heal any damage back so it can use Belly Drum to max its Attack in one turn. It even has the ability to set up Stealth Rocks and or Sticky Web to help the team.
Smeargle @ Focus Sash
EVs: 252 Spe / 252 HP / 4 Def
Nature: Timid (+Spe, -SpAtk)
Ability: Own Tempo
- Spore
- Belly Drum
- Soft-boiled / Stealth Rock / Sticky Web
- Baton Pass
Put something to sleep, max your Attack and pass it on.
Hope I helped.