From Portals of Phereon Wiki
A special trait that can't be passed on. Mounts override the movement of smaller characters on certain biomes on the Overworld. For example, a small sized character with normal movement, who would normally take 15 minutes to cross a mountain tile, can ride a normal sized AirMount with flying movement to cross the same mountain tile in 5 minutes. An equally normal sized character with normal movement does not benefit.
Also see Land Mount, Lava Mount, Water Mount.