Story 1: "The Condemned Legionnaires!"
Satan Girl, a new super-villain, deals the female Legion of Super-Heroes members a deadly virus called the Crimson Virus. The male Legion members call on Supergirl to help out. It is revealed that Satan Girl is actually a clone of Supergirl, who was created when Supergirl was exposed to red kryptonite. The 48-hour time limit of the red kryptonite was over and the clone faded back into Supergirl before she could poison the female Legionnaires to death.
Reprinted in Adventure Comics #409, Adventure Comics #500, The Legion of Super-Heroes Archives #2 & Showcase Presents Legion of Super-Heroes Volume 1.
Story 2: "Father's Day on Planet Krypton!"
Reprinted in Superman #232.