With the Sidney/Wiggly rotating out I haven't found and good synergy.
gotta worry about that fighting weakness. even if GG takes a step back, expect to see gliscor all over the place. therefore i would say that bubble coat and probably snowpoint temple are essentials in a darkrai deck.
And lets face it the only fighting being played is Lucario LV X
GG says hi, it can OHKO darkrai without flipping any prizes and flipping 4 to OHKO your single honchkrow X.
Sorry to say as much as I want to try darkrai, until GG play goes down (which is slim) darkrai will get demolished.
Darkrai will NEVER be more then a good Tech in the current metagame. Even with Snow Point Temple, any Figthing type that has an 60 damage attack KO's it like nothing.
I like him as a great tech in my funny VileKiss deck.
It uses Togekiss as attacker. With Darkrai's 1 Retreat Cost, I can keep him out of harms way while dealing heavy damage with Kiss byDark Engage-ing him with Weavile.
While that is a really good tactic, I have huge trainer card problems and thus is far from perfection.
But if you play honchkrow LV. X it is resistance to fighting and you can use weavile to power it up and then use darkrai LV. X to make each dark energy 10 more and if you want to keep honchkrow safe just use murkrow to do damage using honchkrows attacks