VILEPLUME is supposed to play the role of a HP TANK:
PETAL DANCE: its ev yield is 3 special attack, so its worth training, plus it has a whopping 120 attack, which is dangerous when it come to 3 special attack.
DRAIN PUNCH: healing is important to vileplume, since it has many weakness. its best to give vileplume, a fighting gem OR a black belt, which boosts fighting moves
SLUDGE BOMB: one of vileplume's best poison move, and a special move along with its poison type, this should be a move not to mess with.
MOONLIGHT: who wouldn't want to heal? in a double battle your Pokémon could use sunny day, then vileplume should gain back 12.5 health. not much, but it's worth try.