Here is the full list of all 26 Skyworld achievements.
Complete Mission 1.
Complete Mission 2.
Complete Mission 3.
Complete Mission 4.
Complete Mission 5.
Complete Mission 6.
Complete Mission 7.
Complete Mission 8.
Win a Skirmish match.
Win 5 Skirmish matches.
Win 10 Skirmish matches.
Research 20 unique cards.
Upgrade castle to final level.
Upgrade 20 unique cards to final level.
Win 25 Battles.
Win 50 Skirmish Battles.
Earn 1000 Gold.
Earn 1000 Food.
Earn 1000 Magic.
Built 50 watchtowers.
Have a population of 50.
Walk over 250 steps.
Destroy an enemy castle with 4 cards.
Win a battle with maximum HP penalty.
Take down 50 watchtowers.
Find 8 ducks hidden in the campaign Overworlds.