Just got around to reading this one; here's some initial observations:
- I'm a bit confused about the narrative role of the defenders in this scenario — are they the "nightmares" that exist in the barrier, or the people who inhabit the land that the nightmares shield? Their initial deployment zone suggests the latter but the respawning rule would make more sense for the former.
- I agree that the scenario seems skewed in the defender's favor for the reasons Pluisjen pointed out below.
- "If possible, both halves of the Zone grow in the same manner." — this reads to me like you must choose a direction in which both halves can grow as long as such a direction exists. This would mean that the two halves of the Nightmare Zone can't grow towards each other; is that intended? Also, as a sidenote, this effect should specify how the direction is chosen — I presume it's not the attacker's choice, but can the defender choose or is it random?
- This is a very minor thing but giving the map a solid outline might have made it easier to parse visually.