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