Here is the full list of all 27 Rooks Keep achievements.
Win each game-mode
Defeat an upgraded piece (5 skills at least) without your own upgrades
Win 20 matches
Defeat the attacker in Combat Chess
Kill 10 enemies using Bash
Win a round without losing a life (LMS, TLMS)
Kill 10 characters in one life with the Damage
Eliminate all teams without changing sides (Conversion)
Kill 25 enemies without dying
Kill 10 team members
Defeat a Warlord
Fully purchase all skills
Become the Warlord
Upgrade your character 10 times in the same life
Beat the AI at Classic Chess
Turn your pawn into a queen in chess
Kill an enemy with your ability
Win a match
Win a Team-Match
Kill 10 enemies without dying
Draw first blood
Kill 1000 enemies
Win 200 matches
Win in every arena map
Win in every Chess map
Win a match with 5 mutators running
Win a match as every character (arena modes)