Quick answer
Destroy 100 Grunt backpacks during gameplay; shooting the backpack—not the Grunt—triggers visible gas expulsion and counts toward the achievement.
Guide briefing
Bad Gas Achievement Guide for Halo Campaign Evolved
Destroy 100 Grunt backpacks during gameplay; shooting the backpack—not the Grunt—triggers visible gas expulsion and counts toward the achievement.
Applies to
- — Halo Campaign Evolved campaign play where Grunts appear
- — Players mopping up the Bad Gas achievement or trophy
Target
Understand the Bad Gas requirement
- Checkpoint
- Before beginning a focused cleanup run
- Landmark
- A Grunt with the backpack visible on its back
Do this
- 1Set the target at 100 destroyed Grunt backpacks, not 100 Grunt kills.
- 2Use normal campaign encounters first, because the source notes that this total may accumulate naturally during a playthrough.
Confirmation
You are working on the demonstrated condition when the backpack itself is the object being destroyed.
Target
Register one destroyed backpack
- Checkpoint
- A live Grunt is in view and its backpack can be targeted
- Landmark
- The compact backpack mounted on the Grunt's back
Do this
- 1Move your aim from the Grunt's body to the backpack on its back.
- 2Shoot the backpack and watch the Grunt's reaction before choosing the next target.
Confirmation
A strange flying motion or visible gas expelled from the backpack confirms the demonstrated action.
Target
Reach 100 destroyed backpacks
- Checkpoint
- After confirming the backpack reaction on repeated Grunt targets
- Landmark
- The achievement or trophy notification
Do this
- 1Repeat the backpack shot only when the flying or gas reaction confirms the backpack was destroyed.
- 2Continue until the 100th confirmed backpack destruction triggers the achievement or trophy.
Confirmation
The Bad Gas achievement or trophy unlocks when the demonstrated backpack action reaches 100.