If you were going to flood your home plane with a seemingly unending army of metallic horrors and sophisticated war machines, destroy every living thing you could find, and rip the plane down to its component elements only to rebuild it in your own image, how would you do it?
Would you drive your minions to Dominaria in, say, a station wagon? No. You would not.
You'd order up thousands of these:
Phyrexian portal ship, flight mode
It's a Phyrexian portal ship, designed to make the journey from plane to invasion-worthy plane while maintaining the maneuverability of an airship.
Here's the portal ship in portal-opening mode.
Phyrexian portal ship, portal-opening mode