This spell would temporarily turn troops who pass through it into ghosts, capable of passing through solid objects including walls and buildings. They would have no attacking power while in their ghostly state, and would also not take any damage. As ghosts, their AI would adjust and they would be drawn towards their Avatar defenses or buildings. Barbarians to canons, archers to archer towers, Wizards to wizard towers, goblins to gold storage, etc. There could be limits to which troops are effected by the spell, potentially excluding some higher level troops or dark troops.
Unlike other spells, the ghost spell would compel troops in close proximity to enter the spell radius.
Defenses will continue to see and therefore target these ghosts, so splash damage will occur to non-ghostly troops unlucky enough to be close by.
From an animation standpoint the troops would become pale and transparent, and seem to glide across the ground. Perhaps the whole battlefield would darken just a little when ghosts are in play.
