The Serum Antidote was the main focus of the Unstoppable arc. The Serum Antidote was made by Olivia Cahill. She learned how to make the antidote from her time as Leonardo Da Vinci's apprentice. Apparently, the Serum Antidote only affects those who have taken the Master Serum directly, not those who have inherited the traits granted by the Master Serum and the Ingredient Serums from their ancestors. It was made by Sammy Mourad in Flashpoint, when the Cahills were assembling the antidote to save Amy's life.