Here is the full list of all 16 Banners of Ruin achievements.
Reach 10 Stamina during combat
Win a combat with a combined Party Vitality of 3 or less
Have 30 or more Charge during combat
Play 20 cards in a single turn
Reach a party of 6 characters
Apply 30 Poison in a single combat
Win 50 combats
Complete the Tutorial
Defeat the Garrison Commander
Reach 40 or more cards in your deck
Defeat the Elite Brutes
Defeat the Elite Bruisers
Banish 10 cards in a single combat
Hire a character at the tavern
Defeat 3 enemies in a single turn
Forfeit a character card choice