Collapse Portal

This rare spell allows you to instantly close an active portal at the threshold of a crystal sphere. A mega creature or wildjammer that is only partially through the portal when it is collapsed must make a Dexterity saving throw against your spell save DC. On a failure, they take 10d10 mega force damage. On a successful save, they take no damage. After the saving throw, the wildjammer or mega creature chooses which side of the sphere they end up on.