The cosmic cloud was a moving distortion in space and time that connected two different eras of Mondasian history with each other.
One end of the cosmic cloud reached Mondas when it was ruled by Lizard Kings and still with its sister planet Earth. The other end reached Mondas when it was ruled by Cybermen and far from Earth.
After a Cyber-Scout craft came through the cloud and landed in the Lizard Kings' Mondas, the Lizard Kings sent one of their modified apes through the cloud to discover what was on the other side. This ape crashed in the Cybermen's Mondas and led to the Cyberman becoming curious about the cloud and sending the scout that the Lizard Kings encountered through the cloud. (COMIC: The Prodigal Returns)
