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