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