This appears as a horse saddle, made from the finest of leathers, and encrusted with gemstones. It will radiate magic. When investigated, it will be learned that it saddle allows a horse with rider to move twice as quickly as normal, and go five times as far before needing rest.
When first used in a crisis, however (riding hard while adventuring, or getting into a fight, etc.), the horse will immediately start bucking like a wild animal. It will not stop until the rider is off, either by jumping down, or by being thrown. The rider must make either a Strength, Dexterity, or Skill roll, or a Saving Throw (GM's choice) to avoid getting thrown each minute when this is happening. If thrown, the rider takes 3d6 HP of damage from the fall.
When the horse starts bucking, it will do nothing else -- it won't move forward, no matter what danger might be around it. After this happens the first time, the horse will not allow anyone to ride it at all while this saddle is on it.