Pokemon Black and White has all new pokemon, and honestly, I'm not familiar enough with the game yet to tell you where you can find which pokemon. This is a problem, because I'm looking for a fast way to calculate Hidden Power in-game (I am aware that you can use IV calculators to determine what hidden power you have, but given the nature of IVs, you're outta luck for that method if your pokemon isn't already a reasonably high level and/or you've been keeping track of its EVs as well.)
Back in Emerald, for instance, I could reliably find Poochyena / Mightyena to test if Hidden Power was Psychic, Fighting/Bug, Dark/Ghost. I could then go find a Wurmple to determine if my Fighting/Bug result (super-effective against the Poochyena) was Fighting (also super-effective against the wurmple) or Bug (normal strength).
However, new version, new critters, my old plan no longer works; there aren't any poochyena in the game (or at least, not yet).
Which common wild pokemon can I use to narrow down on the correct type of Hidden Power? (Assume I have access to Fly, and White, if it matters.)
Best Answer
In the more recent games, there are NPCs that you can talk to and they will tell you what type of Hidden Power your Pokémon has. According to Bulbapedia, the locations of the NPCs are:
If you want to find out through combat, here's something I threw together (Disclaimer: there's likely a much more efficient way to figure it out):
1. Battle a Patrat / Lillipup.
Super effective: Fighting. Didn't affect: Ghost. Normal effectiveness: goto 2
2. Battle a Cottonee / Petilil.
Super effective: goto 3. Not very effective: goto 4. Normal effectiveness: goto 5.
3. Battle a Klink.
Super effective: Fire. Not very effective: goto 6. Didn't affect: Poison.
4. Battle a Roggenrola.
Super effective: goto 7. Normal effectiveness: Electric.
5. Battle a Sewaddle.
Super effective: Rock. Normal effectiveness: goto 8.
6. Battle a Woobat.
Super effective: goto 9. Normal effectiveness: goto 10.
7. Battle a Ducklett.
Normal effectiveness: Grass. Not very effective: Water. Didn't affect: Ground.
8. Battle a Sandile.
Normal effectiveness: goto 11. Not very effective: Dark. Didn't affect: Psychic.
9. Battle a Ferroseed.
Normal effectiveness: Ice. Not very effective: goto 12.
10. Battle a Timburr.
Super effective: Flying. Normal effectiveness: goto 13. Not very effective: Bug.
11. Battle a Darumaka.
Normal effectiveness: goto 14. Not very effective: Steel.
12. Battle a Drilbur.
Normal effectiveness: Dark. Not very effective: Rock.
13. Battle a Trubbish.
Normal effectiveness: goto 15. Not very effective: Poison.
14. Battle a Deino.
Super effective: Dragon. Normal effectiveness: Normal. Not very effective: Dark. Didn't affect: Psychic.
15. Battle a Blitzle.
Normal effectiveness: Dragon. Not very effective: Steel.
My thought process (possible types at each stage) is in the revision history of this answer.