Here is the full list of all 17 Nekomew's Potty Trouble achievements.
You've completed the story mode.
You've completed the story mode (slow)
You've completed the extra mode.
You've completed the first level.
You've completed the second level.
You've completed the third level.
You've completed the fourth level.
You've completed the fifth level.
You've completed the sixth
You've completed the seventh level.
You've completed the last story mode level.
You've completed the first extra level.
You've completed the second extra level.
You've completed the third extra level.
You've completed the fourth extra level.
You've completed the last extra level.
You've reached the 160 steps mark in the endless mode.