Which do you think is the best moveset for Darkrai?
I think a darkrai with
-Dark Void
-Nightmare
-Dream Eater
-Dark Pulse
Would be good since A darkrai without a put to sleep move is worthless -.-
At the start of the battle Darkrai's quick speed will let him use Dark void and put the opponents pokemon to sleep
During the round Darkrai's Bad dreams will inflict 15-20hp of damage to each pokemon
Next turn you follow up with Nightmare on 1 pkmn thats about 50 hp taken away a turn
On the 3rd turn use dream eater on the pkmn that isn't having a nightmare to inflict damage and heal yourself incase something went wrong
Continue using using dream eater on tht pkmn until 1 of them wake up then dark pulse them to death
If at some point both pkmn wake up then dark void again but don't nightmare/Dream eat its a waste of a turn just keep dark pulsing

You could try a Special Sweeper because Darkrai's SpA and Spd is better than a Alakazam. With 125 base speed and 135 Sp. Attack, that's way too good to waste on two Special attacks.

You could try-
Dark Pulse
Ice Beam
Thunderbolt
???

And for the last slot, you can pretty much use anything, seeing as Bolt-Beam covers mostly everything. The one problem that you should watch out for with this move set is a . None of your moves will be regularly effective. To counter this, you could teach it Focus Blast in that slot, but I like Dark Void better because of Focus Blast's horrible accuracy.