ONLY USE COUNTER !
If the commander is infantry, put him only cav in front (2 or more commanders, but only the counter).
And when you have no cav, wait for the last trial... that's all.
(wow! what a secret!)
And for archer? In this event, archer counter archer!
(it's in big letters...)
And at the end of the day, check if there are not some commander forgotten in the previous pages, if not, just spend your attempts on the last trial
Just watch that for complete information:
https://youtu.be/X72vrwYLgRo?feature=shared