Battlefield restriction barring offensive magic, reducing the war to spells and counterspells — and enabling exploits.
The land war has quickly evolved into a stalemate: a war of non-offensive spells and counterspells, with fog, Protection Spells, and counter-counterspells but no direct magical attacks. Princess Donut discovers the practical effect at the Southern Front when none of her spells work and only Love Vampire fires. Carl is glad Daughter's Kiss is usable at all, since it counts technically as a self-buff rather than offensive magic.
The ban is also gameable. The Reavers infected their pets with Gurgles before the ban took effect, so its arrival in the trenches counts as an exploit rather than a violation — a soldier notes the system has allowed such iffy workarounds in the past, and that defending mages simply need to do better at keeping infections out. Kristen Cronin's protest that the Gurgles is a magical attack gets her no relief.
The rules regime shaping the entire trench war, and the loophole the Reavers exploit with pre-infected pets.