I'm still stuck on Avenging.
The fails: 11-Skeleking x2, 4-Skelequeen, 14-Dark Omen, 13-Metal x2, 11-Pyramid, 15-Achilles x2, 15-Warrior King, 1-Fire, 4-Fire, 1-Forest, 13-Gentle Knight.
I'd love more advice and thoughts about trying these dragons (13-Valiant, 13-Unruly, 10-Diamond, 10-Fungi) or repeating any of the above.