Wind walk seems a little too long-range, so my vote goes with gaseous form. If we want to jazz it up, maybe the gaseous form can have the effect of obscuring mist?
Snowform (Su): A frostmourn may assume the form of a swirling white cloud of snow. This functions as a wind walk spell, but the frostmourn cannot take other creatures with it, and it cannot increase its speed to greater than 60 feet. A frostmourn may remain in snowform for a toal of 10 minutes each day.