The Z-Bots are the antagonists in the 2007 The Asylum mockbuster Transmorphers and its prequel Transmorphers: Fall of Man.
They are robots that come from an alien planet and they are able to change their shapes and sizes. They come to Earth to invade it and to live on it. In the prequel, they use their machines to change the water and oxygen on Earth in order to be able to consume it. In the first film, they are at war with humanity for 300 years.