Here is the full list of all 20 Nyan Cat: Lost In Space achievements.
Played with a skin other than NYAN CAT
A UFO abduction survived
Stayed on the lowest platforms at least for 30 seconds
A UFO abduction survived 100 times
5 pills collected in a game
x250 score multiplier reached in a game
5 times jumped over a doggy in a game
Stayed on the highest platforms at least for 30 seconds
Ran 25 seconds without collecting any food
Played in a world other than Space
Ran 1000 meters without touching any kind of enemies
42195 meters completed
100 bombs deactivated
2000 bombs deactivated
20 enemies eliminated with Nyan Love
250 enemies eliminated with Nyan Love
100 Cow items collected
Jumped on Gold Platforms 1000 times
Tac Nayn touched 9 times
Played 10 times on Nyan Cat City theme