This Achievement is partially buggy..
To unlock this achievement you need to get 5 stars on a challenge. This Achievement is fairly easy to complete if you have leveled up a few cards, my cards were all level 15 and it was super easy to complete. (I hit the bug though
If your achievement percentage has frozen don't worry I have tried a different method but it all trial and error.
1. Start a Challenge in a new kingdom.
2. Change your home kingdom and start new challenge in that kingdom.
3. Use team 1 with your Hero and 3 other cards in a new home kingdom
4. Purchase new kingdom, Set it to home and Start Challenge
The 3rd one worked for me and my achievment Popped.
Hope this helps.