From Halopedia, the Halo wiki
The Methane Wagon is an unstable, slow, and rickety modified version of the Shadow created by Unggoy. It has a parking brake made of a chunk of wood. The Methane will detonate violently when its structural integrity is compromised due to the volatile infusion-enriched methane stored on it.
Armament and support
The vehicle emits a Methane aura, clouds of infusion-enriched methane, that makes nearby Unggoy aggressive. The wagon can also catapult kegs of Methane that release enriched gas clouds of the infusion-enriched methane.
In 2559, when Yapyap rebelled against the Banished during their battle with the crew of the UNSC Spirit of Fire on Installation 00, Yapyap had a few Methane Wagons under his control, hoping to upgrade them.
Halo Wars 2
Methane Wagons are exclusive to Yapyap and can be made at Banished outposts once the leader power has unlocked them. They perform poorly against infantry, vehicles, aircraft, and structures as they primarily buff allied Grunt units and debuff enemies. They will also explode upon destruction, causing damage to nearby enemy units. In Blitz, Methane Wagons cost 70 energy. Despite being rated poorly against enemy units, Methane Wagons will typically outperform Marauders due to their buffs and debuffs.
Pro and Cons
In Halo Wars 2, if a Spartan hijacks a the Methane Wagon, the 2 grunts will remain in the vehicle. This is the second vehicle where the additional crew members remains in the vehicle while hijacked and continues fighting with the replaced driver.
List of appearances