This solution is 100% written by Marcos Aspira for the Windows Phone version of this game. I asked for permission to use this solution for the Windows 10 version first before posting it. I take no credit.
I found that doing this was the quickest way to unlock the cheevo, I had the conditions below:
- Reached Age 6
- Number of troops at least in 50 and their level at least on 3
- All unique civilization troops unlocked (cavalry and that archer are the best)
- First Bizantine Hero unlocked
Before going to battle I made my army like this: 4x stable cavalry, 4x of each other civilization cavalry (3 each), one catapult and battering ram, 3x hooded archer and 5x infantry
Then I searched for an opponent with no strong defenses at the castle (not towers and stuff around it), but only a single line of walls or a weak spot on them to breach and attack direct the castle.
Finding such player, engage the battle first using the Bizantine hero to break a wall and after he succeds, send all your troops to a full attack to the castle, ignore all towers, catapults and enemy troops.
Most times you can destroy the castle before your troops are defeated, you don't earn too much crowns and the attack ratio is low most times, but doing so you don't have to destroy everything in order to attack the castle.