Here is the full list of all 14 Immortal Tactics: War of the Eternals achievements.
Successfully win 1 area in the game
Successfully win 10 areas in the game
Explore and find a Treasure Chest and make sure to open it!
Have any of your unit to get a Gem
Destroy a Tree and clear the path!
Successfully kill and defeat 100 enemy units
Save a helping hand (or paw)
Successfully kill and defeat the Boss in the Wildlands
Successfully kill and defeat the Boss in the Wildlands in Expert Mode
Successfully kill and defeat the Boss in the Swamplands
Successfully kill and defeat the Boss in the Swamplands in Expert Mode
Successfully kill and defeat the Boss in the Castle
Successfully kill and defeat the Boss in the Castle in Expert Mode
Complete the game and have 100% progress