HP moves

[Sceptile_Master]

Master of the sceptiles here

What do the hp moves do (hp rock, hp ghost etc)

I need to know, and what pokes learn them

[Don't Run With Scizors]

HP stands for Hidden Power, which is a move whose type and power changes depending on a Pokémon's hidden stat genes - it's not dependant on the species of Pokémon.

[Poryhedron]

As for who learns it, if memory serves me right, only Unown learns it naturally. And it's the only move Unown learns. There is, however, a TM, and in Ruby/Sapphire you can buy them at Slateport Market any time after getting the Secret Power TM from the guy in Route 111. The same guy who sells additional Secret Power TMs will sell Hidden Power TMs as well.

You can also get one HP TM in Fortree if you win an old lady's guessing game. In Gold/Silver/Crystal, you can't buy HP TMs, but you can get one in a small cottage north of the Lake of Rage (getting there's a bit of a trick; you'll need Cut.)

[Don't Run With Scizors]

Actually, Meditite and Medicham learn it naturally as well.

Also, every Pokémon that can use a TM can use the TM for Hidden Power.

[Sceptile_Master]

Thanks

How do you work out the hidden genes

[dark_tyranitar]

That's the problem. The "genes" or IVs or DVs are invisible. There are two ways to find out what type your HP is, though. The easiest way is to fight a Kecleon, and it's Color Change will turn it into whatever type the Attack was. The other way is to battle multiple Pokemon, see its effectivity and from there, narrow the possibilities down. I don't know what the fastest procedure for that method is, though. If there's an in-game trainer with Kecleon just wait until they want to battle and use them.

[Sceptile_Master]

Thanks dark tyranitar

you have helped me a bunch

May many shinies be blessed upon your game

[Poryhedron]

The other way is to battle multiple Pokemon, see its effectivity and from there, narrow the possibilities down. I don't know what the fastest procedure for that method is, though.

Thought I'd post this in case it helps someone...I've worked out procedures in GSC and RS to determine Hidden Power's type in the earliest areas of the game. Here's my procedure for Ruby/Sapphire. Start at step A and keep going until you find out what HP's type is; you should be able to get it in no more than three steps. It's not possible to guarantee an answer in only two...unless, of course, you get Kecleon involved.

A: In Ruby Version, go to Route 102 and attack a Seedot with Hidden Power; in Sapphire, go to Petalburg Woods and attack a Shroomish.
Super-Effective: go to step B.
Standard damage: go to step C.
Not Very Effective: go to step D.

B: Go to Route 101 and attack a Wurmple.
Super-Effective: go to step E.
Standard damage: go to step F.

C: Go to Route 103 and attack a Poochyena.
Super-Effective: your Hidden Power is Fighting-type.
Standard damage: go to step G.
Not Very Effective: go to step H.
No effect: your Hidden Power is Psychic-type.

D: Go to route 104 and attack a Flying-type, either Taillow or Wingull will do.
Super-Effective: your Hidden Power is Electric-type.
Standard damage on Taillow: your Hidden Power is Water-type.
Standard damage on Wingull: your Hidden Power is Grass-type.
Not Very Effective on Taillow: your Hidden Power is Grass-type.
Not Very Effective on Wingull: your Hidden Power is Water-type.
No effect: your Hidden Power is Ground-type.

E: Go to Route 104 and attack a Wingull.
Standard damage: your Hidden Power is Flying-type.
Not Very Effective: your Hidden Power is Fire-type.

F: Go to Route 104 and attack a Taillow.
Super-Effective: your Hidden Power is Ice-type.
Standard damage: your Hidden Power is Poison-type.
Not Very Effective: your Hidden Power is Bug-type.

G: Go to Route 104 and attack a Wingull.
Super-Effective: your Hidden Power is Rock-type.
Standard damage: your Hidden Power is Dragon-type.
Not Very Effective: your Hidden Power is Steel-type.

H: Go to route 101 and attack a Zigzagoon.
Standard damage: your Hidden Power is Dark-type.
No effect: your Hidden Power is Ghost-type.