Here is the full list of all 10 Kinect Sports Gems: Darts vs. Zombies achievements worth 50 gamerscore.
First steps! You reached level 1 (or observed another player doing so) for the title of Zombie Nerd.
Reach level 2 (or observe another player doing so) to gain the rank of Scared Survivor.
Reach level 3 (or observe another player doing so) to gain the rank of Zombie Hugger.
Reach level 4 (or observe another player doing so) to gain the rank of Dart of the Dead.
Reach level 5 (or observe another player doing so) to gain the rank of Zombie Hunter.
Reach level 6 (or observe another player doing so) to gain the rank of Walking Dead Stopper.
Reach level 7 (or observe another player doing so) to gain the rank of Dart Demon.
Reach level 8 (or observe another player doing so) to gain the rank of Undead Exterminator.
Reach level 9 (or observe another player doing so) to gain the rank of Zombie Nemesis.
Reach level 10 (or observe another player doing so) to gain the rank of Earth's Last Hope.