This alien organism slowly assimilates entire civilizations of other sapient races by making them dependent upon it for survival. It slowly enslaves the unwitting host race by improving and replacing their existing technology until they no longer know how to live without it. In the form of helpful symbiotic biotechnology, it mingles itself with the host organisms until there is nothing left of the hosts' original genetic make up or their culture except that which the alien organism deems useful for its own purposes.
This illustration shows one of the interstellar transports which the alien organism can fashion itself into to transport host races from star to star, where it often tricks them into waging war on other cultures. Its typical strategy is to then cause the attacking host race to lose the war it tricked them into fighting. This way the victorious new race takes the alien "biotechnology" as one of the spoils of war, thus allowing it to seamlessly infect a new unsuspecting civilization.
Having first seen your Shoggoth, I imagine this also could be used for some of the flying and shapeless sorts of mythos creatures, like star vampires when visible, outer gods or, with more orbs, an Azathoth variation.