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.
No you don't have to.
with a special event
You need an event.
In harbor inn
Glitch for it! On Google type in: Tweaking glitch for Pokemon Platinum. find out how to do it and then Type in: How to get darkrai using the tweaking glitch on platinum.