Calamity

Back when Solar and Gregor were creating the Material Plane, they created a failsafe in case the mortals ever became too strong and killed the gods. What they came up with was Calamity, a weapon so strong that could destroy not only the Material Plane, but the entire Inner Plane and even the Outer Planes. It is said that this creature was so daunting that the two gods immediately regretted the abomination and tried to kill it, but due to the nature of the beast they could merely siphon its essence into a gem and render its body dormant. In order to fully hide the beasts existence, the gods entombed it deep in the core of the world.

After generations, there was only one small tribe of elves who remembered the beast but warned of the threat it posed. It was rumored that were any deity to die at the hands of a mortal, the beast would awaken to punish man for its hubris. Many millennia later, it is said that Calamity waits in stasis below the surface, but the gem containing its essence is hidden in the islands of the North Sea.