Powder is a situational move that doesn't even have a good effect in the situations that you are able to use it. As for Vivillion, I wouldn't recommend using it in doubles/triples unless you have a Pokemon with follow me (this way Vivillion could set up with quiver dance without getting hit). In triples, you could run follow me as well as Pokemon boosting its stats because Vivillion gets the move psych up (so Vivillion can copy the stat boosts). If I were to use it, I would use it in singles running bug buzz, hurricane, quiver dance, and sleep powder (not to be confused with the move powder), with the compound eyes ability. The only weaknesses to this are that you will be walled by steel types and you will be wrecked by priority. If you mean a better quiver dance sweeper, Volcarona is better (it isn't walled by steel types and has better special attack, speed, HP, and defenses). In doubles, I would still recommend follow me if you wanted to use Volcarona.