I like Blazing Skeletons. Just be careful because their auras and on-going damage can get crazy. Depending on your set-up, you could add some tension by bringing in the skeletons on turn 2 or 3. Let the party get set-up and do some damage on the Dragon and then bring in the skeletons from an edge of the map. Now the party has to scramble to reposition themselves and this will probably allow the Dragon to get back to moving around if it was pinned down.