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