Use the Refurbished Demolisher to destroy 150 Decomposed Ghouls, 20 Frostskull Mages and 2 Bone Giants in the Valley of Lost Hope. Speak to Matthias Lehner at the First Legion Forward Camp when you've completed this task.
You're going to use this machine against the Scourge? You're not going to win against them like that.
You can destroy hundreds... even thousands of them. But you won't win. Not out here.
When you're done playing with your machine, meet me to the north. There is an old army encampment. What I will show you will teach you a little bit about who you're up against.
Are you done playing with your war machines?
You see? You killed your fair share, but for every one you destroyed, another rose from the dirt to take its place.
You don't know what you're up against, <name>. Let me show you.
Hop in the demolisher. #1 is Ram, a knockback doing about 20,000 damage. #2 is Hurl Boulder, a targeted AoE with a 70 yard range doing about 13,000 damage, enough to 1-shot ghouls and magi. #3 is Double Speed, 100% movement speed increase for 10 sec.
The bone giants have about 50,000 HP.