The Onslaught Add-on for Call of Duty: Ghosts has 11 achievements worth 250 gamerscore.
Found all intels.
Gain access to the Compound area in Nightfall.
Gain access to the Facility in Nightfall.
Kill the Breeder for the first time in Nightfall.
Kill the Breeder in less than 5 minutes in Nightfall.
Kill 50 Cryptids with the Venom-X weapon in Nightfall.
Complete all challenges and kill the Breeder in Nightfall.
Kill the Breeder while using a Relic in Nightfall.
Kill 5 Phantoms in one game.
Found all the eggs in Core MP's Onslaught Map Pack.
Kill a Rhino with only a pistol in Nightfall.