Planar Overlay
After years of preparation Yawgmoth used a large magical burst to cause the Phyrexian-infested plane of Rath to overlap Dominaria, infusing the plane with its own energies, and causing the Phyrexians to magically appear on Dominaria. Rath ceased to exist as an independent plane. Rathi locations and creatures all transposed themselves on Dominaria, sometimes resulting in bizarre hybrids such as Gaea's Skyfolk (elf/merfolk) and Razorfin Hunter (merfolk/goblin).
Read more about this topic: Plane (Magic: The Gathering)