To unlock "Impossible" difficulty, complete the game on "Hard". To unlock "Nightmare" difficulty, complete the game on "Impossible".
Combo Mania - Complete 3,000 chains.
Destroyer - Kill 50,000 enemies.
Fierce Fighter - Play 5 minutes without losing any health.
Hidden Passage - Collect 4 keys in each world.
Kettenfahrzeug destroyed - Complete the 1st world.
Mankind saved - Complete the 5th world.
Master the Menace - Complete the 2nd world on rank "S".
Top Scorer - Reach a score of 2,000,000.
Windgeist defeated - Complete the 4th world.
Impossible unlocked - Complete the fifth world on "hard".
Nightmare unlocked - Complete the fifth world on "impossible".
Ultimate Key Collector - Collect the 20 secret keys.
Galaxy Superstar - Reach ultimate rank 15, galaxy superstar.