A new variant on the animate - a modular Zombie Lord has appeared. In itself it has the dangers of modular zombies and the ability to organise other undead.
The added danger is when the Lord loses its head - it seeks to get a new body. Gathering zombies around it to form the body, it ends up with a shambling mass of zombies taller than most walls. Any higher than a few stories, and the weight of the bodies begins to collapse in on itself.
As an animate siege tower, even if it takes large amounts of damage from wall mounted galvonic cannons, the collapsing tower may breach the wall, zombies falling over to the far side.