Here is the full list of all 15 One Troll Army achievements.
Hire 30 mercenaries.
Complete all remaining quests.
Earn 10000 materials in total.
Kill the most powerful of the bosses.
Survive at least 30 waves without losses at the Survival mission.
Kill 1000 enemies.
Upgrade tower weapons to the maximum level.
Improve all troll skills to the maximum level.
Upgrade all buildings and towers up to level 3.
Upgrade goblins to the maximum level.
Spend 10000 gold on resources.
Earn 10000 coins in total.
Upgrade all buildings and towers up to level 2.
Kill 100 enemies.
Complete all buildings and towers of the fortress.