Here is the full list of all 9 Gem Master achievements.
Win a match
Win 10 matches against Speedy AI
Win 5 matches against Justice AI
Win 3 matches in a row against Merciless AI
Receive the title of Champion
Win a match with score 650 or more
Lose a match despite scoring 500 or more
Win a match without selecting RED colour once.
Play matches on 25 different arenas