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