There are currently no working DS roms or emulators, but if you want, try searching Google for a DS Emulation with Pokemon Platinum ROM also.
you cant you have to use the action replay
you don't
You can get it for free if you steal it.
no you dont get free rare candies you can cheat on any version with gameshark though to get anything you want
Asking for this sort of thing is ILLEGAL.
no
Yes its free.
Yes
you dont
You can't
You can't get Misdreavus in Pokemon Platinum, you have to trade it through Wi-Fi or get it from someone who has Pokemon Pearl. If Pokemon Pearl can't be found, go to McDonald's as they have free Wi-Fi.
There is no legal way to play Pokemon Platinum online for free. You need to purchase or rent the game on Nintendo DS or borrow the game from someone you know who is willing to lend it to you.