10 Scariest Stargate Episodes Ever
7. Stargate Atlantis Season 3 Episode 9: Phantoms
At the beginning of "Phantoms" one of the Atlantis teams fails to check in after going out to explore a planet. Colonel Sheppard takes a heavily armed team through their Stargate to investigate what happened.
As soon as they emerge on the other side, they find the decayed corpses of Genii soldiers, a human race that often battled against the crew of Atlantis.
Sheppard and his team eventually find their missing team; all of them except their leader were found to be dead. A recording revealed that it was actually the team leader who went insane and killed his team, then called for support from the Human warship Prometheus, which had been destroyed in SG-1.
Eventually, it is discovered that the planet had a Wraith mind manipulator on it, causing any humans who happened to wander into the planet to go insane and begin seeing things. The hallucinations are the usual kind for a sci-fi shows, dead soldiers talking, everyone turning on each other, some hallucinating horrific Wraith encounters, and many normal soldiers kill themselves with grenades or fall into traps, dying horrifically.