The Bloodmount is a fairly large Locust creature that runs along on it's two hands. It uses it's feet to attack you. The Locust can ride on it as gun support (Beast Rider or Theron Guard). They can be easily go berserk once you eliminate their rider, using it's claws to severely damage you. The Locust that rides it will either have a Hammer Burst or a Torque Bow. They can do an extremely large amount of damage on you if it hits you with its feet. The Blood Mounts are included in the Gears of War 2 campaign multiple times and in Horde mode on every 10 Levels (Level 10, 20, 30, 40 and 50).
Strangely, the Gorgon Pistol seems to be the most effective weapon against them.