Ok the answer is yes, but only throught the darkrai event
Darkrai
No.
Nope
action replay
Darkrai.
Darkrai is a Pokemon from Generation IV, and Pokemon ruby is a game from Generation III , so you can only get darkrai in Pokemon Platinum, Diamond or Pearl
You dont catch Darkrai in Pokemon Pearl. You can catch it in Pokemon Platinum at level 40.
You need an event.
with a special event
In harbor inn
No you don't have to.
you can find creselia on moonlight island but i dont know about darkrai.