Decent, but the fights take way too long for my patience in the end. I don't think speeding up the extra stages/trials would affect any tactics involved.
Its obviously some luck involved in the hard badge, but adapting your deck between each battle(since you can see the castle's resources/workers) makes a huge difference. Felt like the luck involved was reduced alot just by adding a bigger % of builders/recruits/mages and removing some inferior cards like spy and sabotage, aswell as reducing the amount of some other cards.
So my tip is a small deck with 5 builder/recruit/mage-cards.
 "Death vs Monstars 2"){kind=icon}
 "Bloons TD 5"){kind=icon}
 "My Pet Protector 3"){kind=icon}
 "Earn to Die"){kind=icon}
 "Get Off My Lawn"){kind=icon}
 "Epic War 5"){kind=icon}
 "Animal RaceWay"){kind=icon}
 "Castle Wars 2"){kind=icon}