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