From Halopedia, the Halo wiki
Bisons are versatile, light armored vehicles that served as combat elements in a number of roles, including armored personnel carrier and recovery vehicle.
Between 2531 and 2537, Serina designed a Bison with a vacuum energy siphon, scientific instrumentation, and cryotech weaponry. As there are no Bisons aboard the UNSC Spirit of Fire, Isabel looked at improving and repurposing the siphon with her own research data on Forerunner vacuum energy cells, but the delicacy and intricacy of Serina's manufacturing template complicates this effort.
Halo Wars 2
Bison Upgrade: Cryo Burst
Bison Upgrade: Heavy Cryo Cannon
Bison Upgrade: Heavy Cryo Burst
The Bison is a hero unit exclusive to Serina. It is a heavily armored and shielded vehicle that works well in conjunction with other cryotech units and abilities. Its Coldsnap Launcher fires experimental cryo shells that damage and chill enemies caught in its area of effect. The Coldsnap Launcher can be upgraded to increase damage, range, and freezing speed. The Bison's Cryo Burst ability allows it to "lock down" and deploy a chilly aura that freezes enemies caught within. They can be purchased at the Armory. Unupgraded Bisons perform well against vehicles, but only okay against infantry, aircraft, and structures. Once the Heavy Cryo Burst upgrade has been purchased, the Bison will perform well against infantry. In Blitz, the Bison costs 220 energy and is a Legendary Unit.
List of appearances