Here is the full list of all 12 Hexic HD achievements worth 200 gamerscore. It takes around 20-25 hours to unlock all of the achievements on Xbox 360.
25 Total Combos
Bonus-Star Cluster
Starflower
75,000 Points in Timed
Black-Pearl Flower
100 Games
5000 Total Combos
Beat Survival
1,000,000 Total Points
Black-Pearl Cluster
150,000 Points in Marathon
Black Pearl