Here is the full list of all 21 Warden of the Isles achievements.
Finish the tutorial missions
Grab the same unit 10 times in 1 mission
Throw a unit over 200 meters.
Kill a fire elemental with a fireball.
Kill 100 enemies with fireballs.
Heal 500 units with healing orb.
Summon 50 Elementals.
Move all movable objects in the Warden's Chamber.
Throw and catch the same unit 10 times.
Throw and catch a fireball 3 times.
Have 3 legions with 15 soldiers each.
Train every type of unit in a single mission.
Hold both an enemy and friendly unit simultaneously.
Kill your own unit by throwing them.
Throw a unit into the sea.
Build every building in a single mission.
Build 10 towers in a single mission.
Defeat Lord Ratyev and his undead armies.
Knock on the same building 100 time in a single mission.
Have a worker perform all 3 tasks in a single mission.
Defeat the ultimate threat facing the Isles of Muhan.