Really PDC? Dragonite is currently ranked #1, so I can't see how you would think it would be a Dark Horse.
As for my answer to the question, I have to say Virizion, specifically the Swords Dance set.
Rain Stall is a huge playstyle right now, with the Politoed/Tentacruel/Ferrothorn core. After a Swords Dance boost, Virizion dismantles the core with Leaf Blade (Politoed and Tentacruel) and Close Combat (Ferrothorn). Close Combat also outright destroys Chansey, another common member of rain stall, at +2. Heck, if it runs Stone Edge, it can significantly weaken Dragonite, doing 45% minimum to 252/0 Careful Dnite without Life Orb. Life Orb can be used for more power, while Lum Berry (my preference) can be used to make the switch in easier (coming in on a Scald hurts).