Playing With / One Twin Must Die

• Basic: Due to a certain culture's beliefs, one out of every set of twins must die to avoid a curse/bad luck.

• Straight: Alice and Bob have twins, Cody and Della. Cody is killed to avoid a curse.
• Exaggerated:
  • Alice and Bob have octuplets, and every single one except Della has to die.
  • Alice and Bob have five sets of twins, and kill one of each pair.
• Downplayed: Cody has to be sent away once he reaches puberty to avoid a curse.
• Subverted: It looks like Cody has to die...and then we learn that because Alice was The Chosen One in her youth, there is an exception for any offspring of hers.
• Double Subverted: and then we learn that Cody and Della aren't Alice's after all, and Cody still has to die.