Here is the full list of all 15 Castle Cardians achievements.
Beat the final boss with General
Beat the final boss with Mayor
Beat the final boss with Potionist
Collect 5000 gold in a single battle
Collect 10000 gold in a single battle
Reach the edge of a map
Play 10 cards in a single turn
Unlock all cards
Unlock all relics
Win a game in 5 waves
Win a game without any unit die
Any unit reach 50 kills
Apply 200 or more Poison on a single enemy
Kill 10000 monsters in total
Win the first battle