This is a free action is available to any rider whether on Horseback or flying mounts. Dismounting is done before or after moving the unit. This will prevent you from moving the unit at great distances while Mounted, then dismounting on the same turn.
One reason why you’ll want to dismount is to minimize the Effective Damage you’ll take from weapons or Abilities that’s strong against Mounted/flying units. Here are some of the other considerations or notes regarding dismounting.
* Dismounting allows the riders to use gauntlet weapons, which they won’t be able to use otherwise.
* Flying units gets -2 Spd when dismounted, but they’ll immediately take advantage of the Terrain effect of the spot where they’re stepping on.
* Cavalry units get +2 Spd when dismounted. They won’t get affected by Terrain effects since it’s already applied to them prior to dismounting.
* Falcon Knights get -1 Str and -2 Spd when dismounted