Here is the full list of all 18 Mixolumia achievements.
Score 500,000 points in Marathon mode
Get a 5x combo
Get 450 clears in Marathon mode
Get 450 clears in Intense mode
Play an Endless game for 10 minutes
Play an Endless game for 20 minutes
Play an Endless game for 30 minutes
Get a 10x combo
Complete Marathon or Intense mode in under 5 minutes
Complete Marathon or Intense mode in under 4 minutes
Score 1 Million points in Marathon mode
Score 2 Million points in Marathon mode
Score 2 million points in Intense mode
Score 3 million points in Intense mode
Score 4 million points in Intense mode
Fill the board without clearing any blocks
Clear the board of all blocks
Get 450 clears in Impossible mode