In my experience solos work better a few levels above that of the party. An equal level solo, even with a few friends, just isn't much of a threat. Out f interest, what were the other monsters doing why the party was focusing fire on the dragon? Were they not able to interfer or make use of the distraction?Well, level 12 vs. a level 12 solo (with allies to make the encounter as a whole level 15).
Rolling twice is the killer there, otherwise the bard had less than a 50% chance of hitting.The bard got to roll twice per round since he is, I believe, a twiceborn leader, which is a warlord paragon path. The dragon's Will was 28, but with +6 level, +6 Cha, +3 item, +1 implement mastery (house ruled in as a freebie, but there anyway), he had a pretty good shot of hitting each round.
Is it fair to say that the party used up most of their resources on this encounter? In which case you could always follow it up with something pretty nasty to shake them up a bit before they get a chance to take a long rest. Nothing like an 'epilogue' fight to make them sweat.
