Uxie; Mesprit; Azelf; Dialga; Palkia; Heatran; Regigigas; Giratina; Cresselia; Phione; Manaphy; Darkrai; Shaymin; Arceus
the list is too long but i recommend going to pokemon.marriland.com/diamond_pearl/pokedex
You can catch Sinnoh Pokemon in Pokemon platinum, but you need to migrate and trade unless you have an action replay
You catch them.
To finish the sinnoh dex (Pokemon platinum's,diamond, and pearl dex) you just need to see every Pokemon not catch every Pokemon.
You can catch and find all the sinnoh Pokemon and when you see all the sinnoh Pokemon you get the national dex and find and catch all the pokeradar Pokemon.You get the pokeradar when you get the national dex.
You catch Garatina, Dialga,Palkiia,and all the lake Pokemon but mainly Garatina
You can't get Thunderus in Pokemon Platinum at all. By then when Pokemon Platinum was made, no one knew that Pokemon Black and White were going to be made.
depending on where you go and what you do you can catch all of them, every Pokemon in existence
No. You can only get 1
Cheat, trade, migrate, catch
nothing happens
you catch all of his Pokemon and raise them