Here is the full list of all 20 Rabisco achievements.
The base game contains 18 achievements, and there is 1 DLC pack containing 2 achievements.
Grab the rainbow star in the first level.
You found all paint bukects!
You found the hidden room!
You cleared yourself in the white paint pool!
You finished the Dark Blue World!
You found all moon's stars!
You found all gems!
You finished the Purple World!
You finished the Pink World!
You literally found easter eggs!
You finished the Orange World!
You finished the Yellow World!
You finished the Beige World!
You finished the Green World!
You finished the Blue World!
You finished the Grey World!
You gave your first steps!
You defeated the slime boss!
You activated the hard mode (no checkpoints)!