Developers and Tom
Honestly your glacier examples are to weak with almost zero impact (yes I know example). Do it right by have it go overboard then have it recede back as needed.
You wiped out the west side of Dwilight, then you can do the same to the rest.
50 to 60 percent would do. I would even let the monsters leak in Dwilight more just to make it harder for the realms there to fight off the incursion. But go BIG!