William caught everything thrown at him, didn't say anything more, and started to flash around.
The threat of the incoming flying monsters was negated and dealt with using the water dragons. So everyone stopped worrying about them and focused on fighting the fending off the ground monsters.
William didn't care about anything else but to collect more mud and store it away. He flashed right and left, collecting even the mud that fell on the ground, away from his holes. He kept doing this for half an hour, even after the formations he laid before got exhausted, even after all of the flying monsters died and vanished, turning into a flood of mud.
Everyone kept fighting while keeping an eye on William. He did nothing else but collect mud, and didn't even take part in the ongoing battles for almost one hour.