Cloud gaming or "What is cloud gaming?" is a running gag among the Creatures as one of the biggest mysteries in gaming history.
"What is cloud gaming?" is a quote from an OnLive commercial that occasionally shows before YouTube videos play. The ad goes "OnLive is cloud gaming. But, what is cloud gaming?" at this point, the button to skip the ad appears and all viewers click it. As such, no one knows how the rest of the ad goes and no one finds out what cloud gaming is.
Started in TreeHouse where Seamus kept asking "What is cloud gaming?" In a vlog from Minecon, Sly gives a tour of his and Seamus' hotel room and points the camera out the window to see the view. They point out the sights outside and Seamus comments that "We're almost as high as cloud gaming in this hotel."
Cloud gaming also makes an appearance during a Creature Game Night in which the Creatures play River Rush on Kinect Adventures, Seamus is playing and lands on a cloud. Kootra chimes in with "What is cloud gaming?" and the others all exclaim how that was cloud gaming. On Sly's turn, they call out "cloud gaming" when he comes to the cloud part. He misses, and Danz says that Sly doesn't know what cloud gaming is, and never will.