You cant you have to buy action replay
You can't get Darkrai in any Pokemon game without cheating or hacking.
it is darkrai or garatina but i do have arceus but you have to cheat to do it hope it helped on i have no idea
You can't get Darkrai in any Pokemon game without cheating or hacking until they make an event for it.
== ==
No, you cannot catch a mew in Pokemon Platinum without cheating.
You need Pokemon Ranger Shadows of Almia.Then you must complete the mission "Liberate the Tower", and then send it to Diamond/Pearl/Platinum, and then you shouldhave Darkrai.
Darkrai can't be found in SoulSilver. If you want a Darkrai in SoulSilver, you'll have to trade it to your game from another game. You can find Darkrai in Diamond/Pearl/Platinum on Newmoon Island in Sinnoh, but you need a Member Card. You can only obtain the Member Card through an event with Mystery Gift activated.
Not without cheating
nentendo event sorry but i dont think its out anymore but i have darkrai
get a darkrai from your friend[note if they want to trade)
you can not catch Darkrai in platinum you can only get it at special events or you can go to GTS and trade someone for it the last option is to get from a friend or use a master ball on a wild Darkrai or on someones caught Darkrai.
You can't unless you hack it into your game 'cause there's no other way to get Darkrai without its special item or without Nintendo giving out an event Darkrai.