Yeah Bonebolt really seems like a sure counter against Darkness; even if they try to OHKO with PU Dragons, they'd have to first hit through Bone Wall and then continue for the next turn to try and kill us off. Only problem with that strategy of course is that before that next turn comes, we can retaliate with Lightnings AND put up another Bone Wall. Torb being able to use upped Dragons complicates things slightly, but that just means he can't use Liquid Shadow at all (since the Infection side effect would take all the Dragons down to 5HP, making them disappear next turn via Lightning). And since he can't use Liquid Shadow, we should be able to easily outrace him with Poison alone.
Mono Darkness is one of the slowest Mono decks in existence, so I know for a fact that Bonebolt would have ample time to set up against it and then kill them off promptly.
Drain Life throws a slight monkey wrench in our plans on both strategies, but I haven't bothered to check and see if they still have those available.
But with Adrenavamps, Devtal, and their Sancstall out of the way, this sounds like a surefire win to me; only testing will prove if I'm right or not.