Here is the moveset for in game:
Nature: Should be Timid or Modest but I'm too lazy to find one LOL
Hold: Leftovers or Big Root
Ability: Effect Spore
- Giga Drain
- Dream Eater
Leftovers is generally the best item. In this case, it's better than big root because big roots are useful only when you're using a draining move on a low special defense opponent.