Here is the full list of all 27 Flatland: Prologue achievements.
Finish the Intro
Finish Level 01
Finish Level 02
Finish Level 03
Finish Level 04
Finish Level 05
Finish Level 06
Finish Level 07
Finish Level 08
Finish Level 09
Finish the game
Collect a hidden cube
Collect 100 coins in a row
Collect 300 coins in a row
Collect 400 coins in a Row
Collect 500 coins in a Row, WOW!
Collect Hidden Cube