Actually, Plague DK weak to the point of being unplayable competitively right now. The ‘Rainbow’ version is OK and fun, but with some bad match-ups and hardly a dominant deck.
In the lower leagues, where it’s one of the free decks that beginners, budget players and the like play because it’s the best option they can afford, perhaps? 
Nice expansion, where can I get one?
Well, if you absolutely must, go play Tony, King of Piracy, you newb!
Absolutely not: she alone shuffles three different plagues, at least another one is needed for that effect.
Well, that’s the idea, although nothing precludes you from playing that OP Reno anyway.
Go on, explain to me how it could be possible (big spoiler: it’s not) in a zero-sum game like this. 