Nice bit of Fluff writing there Trish 🙂
I would make this a Boardwide spell simply because spells and items that target fleeing pieces are very hard to use, as you have to be in the right place at the right time for them to be effective.
Also how about this, if an enemy piece fails a check on the board of any kind, they will instantly scatter +1D6?
In any case, I have added your spell in to the Necromancy Deck.