So what are the practical uses of this move? The facet of killing a random Fire-type Pokemon that is supposed to defeat you is pretty amusing, but I am dubious of the practical uses for the following reasons:
- It only lasts a single turn, and if you Powder on the turn the opponent uses some other move, you effectively just wasted your turn.
- The turn could be better spent using something else, as Powder does not actually do much damage most of the time.
- Powder allows the opponent to get a free switchin to whatever they want.
- Constantly using Powder can make you very predictable, and not constantly using Powder vs a faster Pokemon that can kill you with a Fire-type attack leaves you very open.
While on the flip side, Powder does not really do all that much. It seems to me as if it would only be effective as a one time lure that would also scare the opponent from using Fire-type attacks in general vs that Pokemon.
I can't see many Pokemon that would actually use this move, but maybe you guys see a bit more potential in it.
Most of the issues pointed out boil down to pure mind-games and out-predicting your opponent. A lot of moves suffer from this, so it's not entirely nonviable to use.
As for the bolded part, there is only one pokemon that can learn it anyway, as far as I've tested : Vivillon. And while still situational, if you run any other bug types with more SpA than it, you could drop Bug Buzz for Powder and use a set like Sleep Powder / Powder / Quiver Dance / Hurricane. If your opponent sends in a fire type meant to take out your Vivillon, you could scare it off with Powder and get a free Quiver Dance in, allowing you to proceed to sweep with Hurricane or put a big threat to sleep with Sleep Powder. That's the set I'll use for it anyway, once i make my bug mono-type team for OU.
One hilarious instance I could see happening (albeit very hard to set up and very unlikely to happen) would be putting a fire-type Choice user to sleep with Sleep Powder, trapping them with Infestation, and using Powder once they wake up to watch them helplessly kill themselves.