I gave up. Was stuck on warden for over one day and now on skeletal knight for over a day and a half. Tried all suggestions and used those dragons that worked for others multiple times. Played just about every hour from 5am to 10 -11:30pm, using all free videos each day, and still couldn't finish.
It's ridiculous, we should be able to beat a dragon after the third fight. Each fight should weaken the dragons.