I finally beat Glasswing after about 20 losses (used all those "watch this video to speed up battles" just so I could put more dragons into critical!). I used a level 12 Landworm which I remember working for other people in the past but has never worked for me before. At least it is done now and Nautilus went down to my Metal 15 because that was the last high level dragon with any chance that I even had left!