You would have to wait for a new mystery gift to get Darkrai, it's the only way without cheats.
Nope.
you cant i think you can not
Darkrai.
You can't get him without events or cheats. For Darkrai, Manaphy and Arceus you need a event to capture him.
To get Darkrai simply go to fullmoon island and go on the right side and use surf(or ghost cheat) when you get there the will be an entrance through the trees go through there and capture darkrai!
Get the key from Mystery Gift and open the door in caveport that is locked.
im pretty sure you can't catch it without cheats, its liek shaymin or acreus
Darkrai can be found at Newmoon Island, but you can't do it without cheats. If you use the walk through everything cheat and you are at Full Moon Island, where you can find Cresselia, you have to walk to the right until you get at Newmoon Island. There you can interact with Darkrai.
Girantina, Heatran, Dialga, Mespirit, Azelf, Uxie, Shaymin, Cresselia and probably Darkrai.
use ar cheats
You needed a Nintendo Event to get an item to trigger an event to catch him, but this is unlikely to return.