Complete the following tasks to unlock Apple Game Center achievements.

Achievement	How to unlock
All Missions in Easy	Complete all missions in Easy Difficulty.
All Missions in Hard	Complete all missions in Hard Difficulty.
All Missions in Normal	Complete all missions in Normal Difficulty.
Bomb Master	Complete all missions without throwing a bomb.
Flash Bullet Master	Reach Flash Gun Master Level 5.
Invincible	Complete all missions in Hard Difficulty without dying once.
Killer	Kill 1,000 enemies.
Medals Collector	Collect 150 medals.
Straight Bullet Master	Reach Straight Gun Master Level 5.
Super Killer	Kill 1,500 enemies.