There was a likelihood that the wards were only tuned to repel physical bodies and living entities. "Spirits that do not possess physical form should be able to pass through," he deduced.
This line of thought inspired him to think about what kind of spirit beings he could call upon to aid their mission. He had various he could resort to from his vast experience in necromancy. Finally, he decided on using Nethermagers.
Nethermagers were a rank of extremely powerful dark mages who once ruled various kingdoms in times past. They used their dark arts to terrorise large territories until they were routed by powerful archmages dedicated to the light. These dark mages fled into the shadow realm after their death but their powerful spirits were bound to the shadow realm by the light archmages.