People often complain that you can't get loot out of raids because the victim will always hide all their stuff long before you have time to break through the palisades. But what if you could control a nidbane to cross their walls and take some stuff before it's too late?
The moment a siege engine finishes drying on a vclaim or a pclaim, that claim would be considered under siege. It would then be possible to summon player controlled nidbane thieves who could roam around the claim for a short period of time. Fetter quality would determine how long they would exist before vanishing.