There aren't a whole lot of deck ideas behind Darkrai & Cresselia Legen, at least from what I've seen.
As far as PDL goes, it can be run with Heatran Lv.X to get energy cards back, and you'd have to have a main attacker since PDL doesn't do a whole lot of damage (0). This doesn't help a whole lot, since PDL gets 1-shotted fairly often and it helps your opponent use Twins/Black Belt, but it's an idea.
That said, I haven't seen a whole lot of Legend decks work too effectively. Maybe Lugia, but as a whole, Legends haven't had much of an impact on competitive play.