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