Here is the full list of all 30 10 Second Ninja achievements.
Kill two enemies with one shuriken
Spend 5 seconds or more without touching the ground
Complete the tutorial.
Get your first star rating.
Skip a cutscene.
Fiddle around with the settings.
Finish every world.
Finish every world with 3 stars.
Finish a level with 0.03 or less from your next star rating (or 3 star the entire game)
Die over 50 times
Restart over 500 times.
Toggle off the leaderboards OUT OF SHAME
Wander around a level for its duration without murdering anything.
Try firing your shurikens in a boss fight.
Go into the light.
Drop a falling block on an enemy's head
Make an icicle fall on an enemy's head
Press restart before the timer has even begun
Shots... Shots Shots Shots Shots - die on spikes five times in a row
Finish the first world
Finish the second world
Finish the third world
Finish the fourth world
Finish the fifth world
Finish the first world with a 3 star rating
Finish the second world with a 3 star rating
Finish the third world with a 3 star rating
Finish the fourth world with a 3 star rating
Finish the fifth world with a 3 star rating
Finish Hard Mode and bleed the game dry for content