... a spaceship come through hyperjump?
... a monster come from some netherworld?
... a snackfood come out of machine?
You decide what this "thing" is, and you determine the nature of this "portal".
Don't settle for something half-assed... demand at least six-tenths of an ass from yourself and craft a mighty solution to this latest puzzler come courtesy of your trusty topic technician.
You can do it. I know you can.
Open-ended: THE THING COMES THROUGH THE PORTAL