From Halopedia, the Halo wiki
The mountain runner is a multi-legged all-terrain vehicle(ATV) used by the Castoff faction of humans on the planet Netherop. The true origin and manufacturer of the vehicle is unknown, but John-117 suspects that the vehicle was made by an extinct alien species.
The mountain runner is often described as a "spider-machine" by Blue Team prior to its real name being revealed by the Castoffs. It has an oval-shaped body slightly larger than a Warthog with ten protruding legs and a sickle-shaped antennae, which houses its deadly microwave-beam weapon. Inside the riding compartment, up to ten passengers can fit. In the back of the unit are a trio of coal bins leading up to a pipe while the controls were in the front, featuring a thick glass column ending in a transparent orb. The entire compartment is encircled by a meter-high wall.  The coal bins were used to charge the battery that, in turn, powered the vehicle.
In the year 2526, during the Human-Covenant War, Blue Team encountered several mountain runners on Netherop being deployed by the local Castoff faction. While the mountain runners were initially hostile, after striking a deal with the Castoff leaders by offering them a Sharpfin-class escort corvette and a way off the planet in exchange for their cooperation, the Castoffs agreed to support Blue Team in their mission to fight the Covenant.
List of appearances