Unown can't learn other moves besides Hidden Power.
shards can be used to trade with other people. in return, they may teach your Pokemon moves. there are 3 move tutors in Pokemon platinum that will teach your Pokemon moves in exchange for shards in a specific color.
it just a really powerful attack that can only be used after you use all the other moves your Pokemon knows in battle
Meganium does not learn vine whip. Meganium learns other grass type moves such as razor leaf, magical leaf, petal dance, and petal blizzard.
The Pokemon that can learn Thief are listed at this site: http://bulbapedia.bulbagarden.net/wiki/Thief
u have to go to my Pokemon in the trainer HQ then click on the Pokemon then go down to the moves and check them u can only know 4 moves to learn a TM it is the same thing but the TM's are below the other moves.
Hippowdon is a Heavyweight Pokemon and can learn sand attack, earthquake, fissure, and bite. Other moves are tackle, and ice fang.
Dragonair is a Dragon Pokemon who can learn toxic, rain dance, thunder, and surf. Other moves include confide, and swagger.
Catterpie, Roselia, Scyther and many many more grass type Pokemon can learn bug type moves.
Spiritomb is a Forbidden Pokemon and can learn moves such as dark pulse, shadow sneak, and ominous wind. Other moves include shadow ball, and feint attack.
Unown can't learn other moves besides Hidden Power.
Level 20 is when it learns Spark, and then he starts to learn all sorts of other moves like Discharge.
The same moves that it can earn in any other Pokemon games.
Probopass is a Compass Pokemon and can learn stone edge, power gem, and magnet bomb. Other moves include rock blast, and rock slide.
If they are not level 100, they have the ability to level up and learn moves that you don't want your Pokemon to know. My advice is that you keep your Pokemon with you. You can keep a Ditto in there if you want because Ditto cannot learn any other moves beside Transform.
you can go to a move relearner for pokemon emerald it is in fallarbor town i dont know where it is in the other games
the best moves on Pokemon are only for these Pokemon dialga = roar of time palkia = spacial rend giratina = shadow force arceus = all of the above plus jugdement as you can see, arceus is the only one who can learn all these devastating moves, while the other three can only learn certain moves (unless u cheat)