Gear REX is the final giant monster Big Boss encounters during the Monster Hunter side missions in Metal Gear Solid: Peace Walker. It is fought a total of four times, twice on Isla del Monstruo, once in Mount Irazu (location of the Pupa battle) and lastly aboard Mother Base itself (location of the ZEKE battle). Gear REX's name and appearance is an obvious reference to Metal Gear REX , and is the only monster in the Monster Hunter missions who doesn't appear in a Monster Hunter game. It's capable of firing acidic mucous from the protrusion on it's side, similarly to Metal Gear REX's railgun. It also fires spines from it's side and vibrates them with it's roar, stunning players. The in-game description of Gear REX states it was a result of nuclear testing, which is a nod to Godzilla. Chico's description of Gear REX describes it as some sort of zombie dinosaur, although when scanning it with the Analyzer it shows no data.
By S-Ranking any Gear REX mission the player receives Gear REX Fatigues, which allow you to steal Psyche from choking enemy soldiers. The only way to S-rank these missions is to tranquilize Gear REX using the Mk 22, Mosin Nagant or sleep grenades. There are also rare drops which can be used in conjunction with a Tigrex fang to make the "Ultimate CO-OP Weapon" Human Slingshot. By completing Gear REX Strikes back, the cookbook can be developed, this works similarly to the magazines in the game but only affect monsters.
|Gear REX Mucous||Extra Ops 125: Gear REX Battle||Slingshot Band Rank 1|
|Gear REX Concentrate||Extra Ops 127: Gear REX: Showdown at Crater Base||Slingshot Band Rank 2|
|Gear REX Super Extract||Extra Ops 128: Gear REX Strikes Back||Slingshot Band Rank 3|
|Cookbook Research Notes||Extra Ops 128: Gear REX Strikes Back||Cookbook|
|Gear REX (Uniform)||S-Rank Extra Ops 125-128|