Play mission 3 on co-op with two players. There are two secret switches that are marked as "doors" that you can open, both of wich can be found after Rally Point Alpha (where you must destroy the Wraiths). Switch "A" is on the coast of the water southeast of the buildings with a pair of switches that you must activate. The switch on some rocks near the frozen waterfall. The message "Hold X to Open Door" will appear when in the correct location. Note: Reload your weapon before finding it. Switch "B" is past the AA cannon in the next area. Find a pile of rocks with some trees on it that overlooks the walled complex on the ice that is below the area. With both players standing at those locations, press X simultaneously. The message "REACH RACER" will appear. You will then be transported to the Oni: Sword Base with two Gauss Cannon Warthogs. You can race the other player through a course marked by red waypoints. The losing Warthog will explode at the end of the race.