Here is the full list of all 11 Legendary Knight achievements.
Finished Wave 25 in the Village.
Finished Wave 50 in the Fortress
Kill 50 enemy.
Kill 250 Enemy.
Kill 700 Enemy.
Kill 1500 Enemy.
Train 10 Soldiers.
Train 50 Soldiers.
Collect 2000 Coins.
Collect 15000 Coins.
Send 25 soldiers to their deaths.