The transmuted creature can tread on air as if walking on solid ground. Moving upward is similar to walking up a hill. The maximum upward or downward angle possible is 45 degrees, at a rate equal to one-half the creature's normal speed.
A strong wind (21+ mph) can push an air walker along or hold her back. At the end of her turn each round, the wind blows her 5 feet for each 5 miles per hour of wind speed. The creature can, at the DM's option, be subject to additional penalties in exceptionally strong or turbulent winds, such as loss of control over movement or suffering physical damage from being buffeted about.
The character can cast air walk on a specially trained mount so it can be ridden through the air. The character trains a mount to air walk with the Handle Animal skill (air walking counts as an unusual task).