195. Underground Lake
The army of 20,000 plus undead were slowly marching towards the castle as news of Mammon's demise had yet to reach them. It was fairly easy to surmise that Mammon had something to do with this army as well because the timing of their movements were too perfect.
Tyler had regularly received reports from Flare and Kali of the undead king's movements at a Fixed schedule he had set for himself. So naturally, he was aware Zerahut was gathering corpses to fill his forces. Last he heard, there were only around 3,000 weak undead but in the span of a few days, that had suddenly grown to 20,000 so it was obvious someone else had helped him.
While their March was slow, they were still undead creatures that didn't require food or sleep and could move all day and without rest.