The Forces of Nature Add-on for Gears of War 3 has 10 achievements worth 250 gamerscore.
Build or repair 50,000 worth of fortifications as Mechanic Baird LE.
Complete all 50 waves of Horde on any of the Forces of Nature maps.
Complete 20 consecutive waves of Horde on any Forces of Nature map without going down or dying.
Complete all 12 waves of Beast on all Forces of Nature maps.
Get 25 kills with any of the hidden elementally charged Cleavers in Horde.
Achieve the maximum level on all fortifications in Horde mode.
Win a match of Guardian on all Forces of Nature maps.
Bag and Tag 20 opponents while playing as the Savage Hunter in Versus multiplayer (any mode).
Kill 10 opponents as the leader in a round of Guardian on a Forces of Nature map.
Kill a Lambent Berserker with a team comprised of 5 Forces of Nature characters in Horde.