I imagine deception will play an important role in GvG wars, mostly infiltration and sabotage. There's a lore snippet in the Races spotlight in which a turncoat turns the tide of a siege battle:
One blink, two blinks, then more every second. Mae could see the brief flashes of purple light coming from every street in the dark of the eclipse. The mages were calling it a day and teleporting god-knows where. The town was lost, now that was for sure.
There had been hope before, even when the light of day had started to fade at the wrong hour of the day. They were prepared. The walls surrounding Omenia were strong, and everyone had a great deal of faith in those shining tubes of iron they had put up there on the bastions. They could shoot large spheres of metal right in the middle of the sieging army, the engineers said. And then there was the main door of course, an unbreakable monster of wood and iron. Too heavy to be handled by human or animal power, it was controlled by a massive steam engine – another novelty of the twisted times they lived in, she thought. It could have all worked out, hadn’t she ordered her little rebel unit to murder the technicians and seize control of the engine. Soon after, the main door had swung open, throwing the whole garrison of Omenia into dismay.
Mae turned around to a rumbling sound getting closer to her apartments. They were coming. She could hear the screams of agony of her guards and servants. A bitter sacrifice, but one for a good cause. Bad things must be done at the call of a superior good.
The ravaging beasts that entered the bed chamber found her naked, glaring back at them with impassive green eyes. They were still hungry – always hungry – but didn’t dare to make a step further. They had been ordered not to do so, and while they didn’t always respect orders, that time surely they did. Then they moved to the side, swift and respectful.
Mae watched them pave the way for their master – and soon she made her appearance. She was so beautiful, slim, tall, with shining white eyes that seemed to eat all the light in the room. Mae had waited so long to meet her. Shaking a little – but just a little – she started walking towards her, then broke into a run, ending up straight into her arms. It was a moment of pure joy – no, more, ecstasy! – when she finally felt the teeth slowly descending into the flesh of her neck.
