No, the only way to capture Darkrai in Diamond or Pearl is to obtain the Member Pass Key Item from a Nintendo event. At the time of writing, this event has yet to happen. Several Darkrai have been given away at Toys 'R Us in America and Woolsworth's in the UK. Those Darkrai are currently the only legitimate Darkrai.
no
You need the darkrai event to happen so you can get the item to access darkrai's island. When you get the "hotel key" go to the locked hotel in the city where you can access iron island from. Spend the night there and when you wake up you will be on a island (new moon island) and if you travel a bit further in you will find darkrai. I will advise bringing a Pokemon with false swipe, it makes your life so much easier!
bait
Go to the Trophy Garden which is in the Pokemon Mansion. porygon is rare in Pokemon Diamond, so using the Poke Radar would be easier.
when you find that Pokemon if you have a master ball with you use a pokeball and you will capture it
Migrate from FireRed. It's easier to get Paras in THAT game.
A Pokemon's catch rate can range from 3 (hardest to catch) to 255 (easiest to catch). Hardest to catch (catch rate = 3): - Uxie - Mesprit - Azelf - Heatran - Regigigas - Giratina - Cresselia - Manaphy - Darkrai - Arceus Easier to catch (catch rate = 30): - Dialga (& Palkia) Easiest Sinnoh legendary to catch (catch rate = 45): - Shaymin
Its much easier to trade for it, You need a special event to get it in your game
Go to Miracle sea and bring a secret slab or a mystery part with you and he will ben in the 3 floor. too bring a golden mask with you, that will be easier to recruit defeated Pokemon
If you already beat the game, just battling the Elite Four is a great way if you can take the repetition!
It's easier to start a new game.
I would get a Pokemon with the move false swipe (e.g. Gallade,Sceptile etc) and also carry a lot of Ultra balls with you to increase your chances of catching Pokemon.