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There are 12 achievements in Defender worth a total of 200 

Picture	Achievement	Description
	Mutant	Shoot 5 mutants in one game.	10
	One Wave	Make it to the 2nd wave without losing any humans.	10
	Cooperation	Achieve a score of 15,000 during an Xbox Live CO-OP game.	10
	Competitive	Win 30 Xbox Live versus games.	15
	Nice Catch	Rescue a human with a mid-air catch.	15
	Getting Better	Make it to the 3rd wave.	15
	Fifteen Grand	Obtain a personal score of 15,000.	15
	Run!	Survive the first 75 seconds without shooting, bombing, or teleporting.	20
	Baiter Bane	During an Xbox Live Co-op game, kill 5 baiters in any level without using any smart bombs.	20
	Five Waves	Make it to the 5th wave.	20
	Twenty-Five Grand	Obtain a personal score of 25,000.	25
	Protect All Humans	Lose no humans in the first 3 waves.	25