Complete the following achievements to unlock Microsoft Gamerscore points.

Achievement	How to unlock
99 Problems and a Zombie Ain't One (50 points)	Reach a combo of 99 kills in any mode.
A Survivor is Born (100 points)	Reach wave 10 in Survivor Mode.
Airborne Appendages (50 points)	Get 20 projectile kills in a single stage.
Blistered Feet (100 points)	Complete Marathon mode.
Bow to me (200 points)	Attain 5 stars on all story stages.
Can't Touch This (50 points)	Finish a stage without taking any damage.
Flying Blind (50 points)	Finish a stage with the crosshair off.
Half Marathon (100 points)	Reach Stage 2-5 in Marathon Mode.
Insert Coin (50 points)	Complete your first level.
No cat left behind (100 points)	Complete the final stage and story mode.
On Rails (50 points)	Finish a stage without ever changing lanes.
Pacifist (50 points)	Finish a stage without killing a single enemy.
Pound Cake (50 points)	Kill 10 enemies with one sledgehammer power-up.