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