Here is the full list of all 50 The Walking Dead Onslaught achievements.
Finish Chapter 1: Desperate Days (Veteran)
Replay and Finish Any Chapter from Chapter Select
Complete all of Oliver's Requisitions and Fully Upgrade the Clinic
Fully Upgrade all Buildings in Alexandria
Complete Alexandria (Max Population, Buildings Fully Upgraded, Campaign Complete)
Reach Maximum Population (25) in Alexandria
Finish Chapter 7: The Promise (Any Difficulty)
Finish all Campaign Chapters (Any Difficulty)
Discover all Weapons for the Armory
During Evac, Survive for 3 minutes after the Van Arrives
Complete All Scavenger Sites
Construct all Buildings in Alexandria
Unlock all Scavenger Sites
Finish Chapter 6: When Dust Settles (Any Difficulty)
Kill 1,193 Walkers
Finish Chapter 5: Roads Less Traveled (Any Difficulty)
Kill a Spike Walker
Kill 5 Walkers With One Explosive Trap
Choke 30 Walkers
Fully Upgrade Any Weapon in the Armory
Finish Chapter 4: Around the Bend (Any Difficulty)
Bring 10 New Survivors to Alexandria
Complete all of Rajul's Requisitions and Fully Upgrade the Town Hall
Finish Chapter 3: The Rabbit Hole (Any Difficulty)
In Scavenger, Get to the Rendezvous Point Without Taking Damage from the Wall
Finish Chapter 2: Strange Circumstances (Any Difficulty)
Kill an Armored Walker
Discover a New Weapon for the Armory
Finish Chapter 1: Desperate Days (Any Difficulty)
Complete a Scavenger Site
Find a Supply Cache in a Supply Run
Upgrade a Weapon in the Armory
Construct the Town Hall in Alexandria
Bring a New Survivor to Alexandria
Finish Prologue: What Comes Before and After (Any Difficulty)
Finish the Tutorial
Finish Chapter 2: Strange Circumstances (Veteran)
Finish Chapter 3: The Rabbit Hole (Veteran)
Finish Chapter 4: Around the Bend (Veteran)
Finish Chapter 5: Roads Less Traveled (Veteran)
Finish Chapter 6: As Dust Settles (Veteran)
Finish Chapter 7: The Promise (Veteran)
Finish all Campaign Chapters (Veteran)
Kill A Walker With Every Weapon in the Game
Earn All Achievements
Complete all of Hazel's Requisitions and Fully Upgrade the Stockpile
Complete all of Sydney's Requisitions and Fully Upgrade the Windmill
Complete all of Julia's Requisitions and Fully Upgrade the Forge
Complete all Requisitions
Fully Upgrade All Weapons in the Armory