These Energy beings inhabited the planet M5S-224, although they did not originate there. To outsiders, they appeared as a nondescript white fog permeating the air around the planet's Stargate; however, in reality they were intelligent beings that were killed en mass whenever the opening Stargate released its unstable vortex.
When Major John Sheppard's team and Dr. Elizabeth Weir came to the M5S-224 intending to dial Earth, which would endanger even greater numbers of them due to the energy required to dial another galaxy, the lifeforms took preventive action. While the intruders were made to believe that they successfully returned to Earth, their minds were actually trapped in a hallucination constructed from their memories of Earth (With the exception of Teyla Emmagan, who 'shared' Major John Sheppard's illusion as she had no memories of Earth to draw on).
However, despite the creatures' attempt to create a convincing illusion to keep the crew confined to Earth, various anomalies emerged in their respective hallucinations; Doctor Rodney McKay noted that the Zero Point Module had experienced an impossible malfunction when the illusionary SGC attempted to discourage him from using it to dial the Pegasus Galaxy, Doctor Elizabeth Weir observed McKay acting out of character, and Major Sheppard's unusual ability to control the creature's illusions resulted in him interacting with various dead comrades and past crushes. One of the lifeforms, who assumed the identity of Major General George S. Hammond, eventually revealed the masquerade and agreed to free them in exchange for them leaving the planet and abandoning the plan to contact Earth. Sheppard assured them that they would not sacrifice the creatures to get back to Earth. (SGA: "Home")
- In an alternate reality, the energy beings of M5S-224 likewise deceived the First Atlantis Reconnaissance Team and Dr. Weir into believing that they had successfully returned to Earth. After arriving in our reality, the Lt. Colonel Cameron Mitchell of this reality cited this incident as evidence in supporting of his theory that the Stargate Command of our reality was an elaborate alien deception. However, it was later revealed that the SG-1 of this reality were responsible for the convergence of the various realities. (SG1: "Ripple Effect")