Tyris had destroyed everything in one go save for the cornerstone containing the pseudo cores of the lost city. It was supposed to cause a massive energy loss that would weaken Thaymos while also ensuring that the damage wouldn't trigger a chain reaction and endanger her children.
Yet the Eternal Fortress' core was still burning with power.
Too much power for what measly amount he could draw from the thrice-occupied mana geyser. Way more power than even the collective cores that the monsters of the Black Tide possessed.
A power stronger than Thaymos possessed a few seconds ago when Tyris had stepped on the battlefield. Due to Fenagar's interference, the Great Mother needed some effort to spread her breathing technique, Mother Earth, throughout the battlefield and understand what was happening.