Flowstone is a memetic, animated, rock-like substance able to obey commands and warp into whatever shape is needed. It is magically animated stone that has attacked, afflicted, and allied with mages across three planes.
It has also formed crucial aspects of Dominaria’s history. Yawgmoth, with the help of his subordinate evincars, cultivated an expanse of flowstone on the plane of Rath. This flowstone expansion caused Rath to overlay Dominaria—all part of Yawgmoth’s plan of invasion. The planar overlay brought with it hordes of Rathi creatures, which then became permanent fixtures of Dominaria.
On Rath, the Flowstone was created by a flowstone factory within the Stronghold. Magma from the Furnace of Rath is sucked up in a tightly concentrated stream by massive levitors at the Stronghold's base. The magma enters a rotating housing that breaks it down, grinding and siphoning it through increasingly smaller mechanisms until it reaches almost microscopic proportions. Each mote is re-engineered as a fantasy nano-machine while still retaining stone-like qualities; several different varieties of flowstone motes exist. It is then subjected to a series of arcane stages where it is bombarded by vast energies. Then the material is purified in a "buffer cyclone", which separates the flowstone from a black tar-like impurity; this impurity is ejected into the Death Pits of Rath. The purified flowstone spews out, pushing the older flowstone outward, and congealing across the entire world's surface.
It may look like soil, but its nature is malice.
"Like an avalanche. With teeth. That will chase you. Uphill." -Flint Foot, viashino runner