You can't catch Shaymin in sky form, but you can find the land form and then change it. You can find Shaymin in land form in Flower Paradise in Sinnoh. Flower Paradise is an event-only area and you'll need Oak's letter (which is an event item). After you've caught Shaymin in land form, you need to visit the Flower Shop in Floaroma Town. A blonde woman near the Flower Shop will give you the Gracidea Flower. If you give this to your Shaymin, it will transform to sky form. However, it can't stay in sky form during the night, when he's in a PC or when he's frozen.
give it the gracida flower
You can't catch whismur in Pokemon pearl or diamond but but you can catch its evolved form loudred with the pokeradar on the top of mt coronet.
To get a Giratina in Pokemon Diamond, you'll have to catch it in Pokemon Platinum, then trade it to Diamond. However, when you catch it in its Origin Forme and trade it to D/P, it'll revert back to its original form, due to Pokemon DP not having the Giratina Origin Forme sprite programmed into the game.
Catch a Burmy and battle with it caves, ruins or on a road.
You can't catch a Dragonite but you can catch it's first evolve form Dratini in certain lakes at Mt. Coronet with a super rod.
Poochyena cannot be caught in Pokemon Pearl. It's evolved form Mightyena however can be caught in Pokemon Diamond on Routes 214 and 215 with the Poke Radar.
you can probably find it on trees. or you could trade it over form diamond, platinum, heartgold, soulsilver, or RSE.
It depends what game you have. In diamond/pearl you can't. In platinum, if you make it faint (not kill, Pokemon can't die) you cab't catch it, BUT you can catch again its its ALTERED FORM (which looks cooler).
The Pokemon Dusclops evolves from the form Duskull at level 37. This Pokemon has a relatively high catch rate, so finding one in this game should not be that difficult for you.
Ambipom, which is the evolved form of aipom
The meteors in Pokemon Diamond can change Deoxes's Form. (Attack, Defence, Speed, and Normal.)
Barboach.