The Zomboss Down Add-on for Plants vs. Zombies Garden Warfare (Xbox 360) has 10 achievements worth 250 gamerscore.
Grow a Doom-shroom, Bamboo Shoot, Fire Peashooter and Ice Peashooter
Vanquish 500 Pirate Zombies
Be on the Winning Team for 15 matches of Gnome Bomb
Push the Golf-Bomb into the Hole in Cactus Canyon
Summon a Barrel Pirate and Map Pirate Zombie in Gardens & Graveyards
Plant 5 Gnome Bombs
Defuse 3 Gnome Bombs
Vanquish 10 Enemies while They are Carrying a Gnome Bomb
Defuse a Gnome Bomb with Less Than 3 Seconds Remaining
Pick up a Gnome Bomb