Normally, units cannot be carried by other units, but some effects allow it, e.g. War Horse. Such effects are worded 'may carry...' or 'can pick up...' or similar, but all work in the same way. Such units have modified Pick Up and Drop basic abilities, as described in those codex entries. If such a unit loses the ability to carry other units, the carried units are immediately dropped. A unit that's being carried must share at least one location with the unit that's carrying it. If they ever share no locations, the carried unit is automatically dropped. Similar to carrying artifacts, the carried units are moved along with the unit that's carrying them. This is considered forced movement. If a carried unit cannot enter the location, the carried unit won't move (and will be dropped as usual if they no longer share a location with the carrying unit). For example, if a War Horse tries to carry a Bosk Troll into a Gnome Hollows, the War Horse can enter the Gnome Hollows but the Troll cannot, and thus the Troll remains where it was and is automatically dropped. Units that can carry other units confer Airborne, Burrowing, Submerge, and/or Voidwalk to the carried units while they're carried. For example, Phantom Steed can pick up a Bosk Troll and then carry the Troll into the Void. The Troll will have Voidwalk while being carried by the Phantom Steed, and thus be able to survive in the void. Carried units may take the Move and Attack action normally (once the Storyline is empty). Therefore, even if the carrying unit can't Drop that turn, the carried unit could still move themselves normally. For that first step, they will have any movement abilities conferred to them by being carried, which are lost as soon as they're no longer carried. For example, a Bosk Troll on a Phantom Steed in the void could step from the void onto the surface of an adjacent site, using the Voidwalk ability conferred to them by being carried. Once the Troll is on the surface of a site, it's no longer being carried by the Phantom Steed, but by that point it's safely out of the void and on the surface.