How do you beat darkrai I am a riolu and my partner is shinx and shinx..

Get lots of Reviver Seeds, Violent Seeds, Oran Berries, and link your moves.

Bring:
Oran Berry (10)
Reviver seed (3)
Stun seed (1)
No Money
Isomniscope (2)(Only if you and your partner don't have nonsleeper)
TM Thunderbolt (Teach Shinx it)
TM Dig (Teach Riolu it, works against all except Mismagius, super effective against all enemies except Mismagius and Darkrai.)
Make sure Shinx knows Discharge and you know a Fighting-Type move and Bite. If you don't know bite, use TM Dark Pulse on yourself.

First, have shinx use discharge. Then, throw a stun seed at Darkrai and take out enemies that weren't defeated by it. Use Dig and whatever fighting type move you know, and set Shinx's tactic to "Go after foes" and register all moves for it. If Cresselia is low on HP, give it an Oran Berry and switch places with it the next turn. Knock out Mismagius with Dark Pulse, which is super effective against it. Once you've defeated everyone except Darkrai, heal your team and use only your fighting type move and dig against it. Also, move to a position where Cresselia can't be hurt, since Cresselia is the weakest of all of you. I beat it with that strategy, actually. I borrowed my friend's AR and did the fight with a Riolu and Shinx I recruited and won with that trick, same levels, no editing of stats or other cheats to give me an edge in-battle.