yes,you can battle with any Pokemon game that's for the ds/dsi/the new 3DS.
Yes, Pokémon Platinum was created to be a Nintendo DS game so it can be played on all of the Nintendo DS systems which includes the original Nintendo DS, the Nintendo DS Lite, the Nintendo DSi, the Nintendo DSi XL, the Nintendo 3DS and the upcoming Nintendo 3DS XL.
yes it works with any diamond pearl or platinum game
try it again and if that doesnt work you need to catch every Pokemon
Sadly no, Nintendo tried its best to stop all the use of AR on Pokemon Platinum. But hackers found out how to crack the game. But their are many codes out there for Pokemon Platinum that are similar to Pokemon Pearl. You just have to look on the AR website.
Pokemon Platinum is a DS game, therefore works on the DSi, DSi XL and the 3DS also.
Pokemon platinum can work on NDS
The Nintendo 3DS is backwards compatible with Nintendo DS titles, so all DS Pokemon games and subsequent 3DS Pokemon games will work on the 3DS.
Trading cards will not work in 3DS console.
yes
Pokemon Black is a regular DS game and will work in any DS, DSi or 3DS model.
yes,you can battle with any Pokemon game that's for the ds/dsi/the new 3DS.
Pokemon LeafGreen was made for the Gameboy Advance, and so yes, it will work on that system. It will also work in a Nintendo DS that has the extra slot (3DS and later do not have the extra slot), where you can play from that slot or migrate past Pokemon to Diamond, Pearl, or Platinum.
by pressing 'work'
No it doesen't
I HIGHLY doubt Pokemon Pearl AR cheat codes will work in Pokemon Platinum =]
It will work, but Nintendo says there will not be any special features specifically for the 3DS.