Here is the full list of all 12 Arcadium achievements.
Get the ball upgrade.
Get the barrier upgrade.
Get the laser upgrade.
Get the ball, barrier and laser upgrade in one playthrough.
Get 50 000 points.
Get 100 000 points.
Get 150 000 points.
Get 200 000 points.
Beat the game on easy mode.
Beat the game on normal mode.
Beat the game on hard mode.
Beat the game on hard mode without upgrades.