Medusa's Head

Medusa's head is fatal to anyone that looks directly at it, even if she is dead. This was originally a punishment to her from Athena after she desecrated her temple with Poseidon. Anyone who looks at her face will turn to stone, even if her head is chopped off. Perseus, son of Zeus, cut off Medusa's head as a wedding present for King Polydectes, only find out the wedding was a trick to take Perseus's mother. You can only look at Medusa's eyes from a reflection, otherwise you're turned to hard, cold stone.

Appearances
Percy Jackson once sent Medusa's head to his father, who sent it back to him. He then gave it to his mother so she could turn her abusive husband to stone. After, she sent the stone statue (of her husband) to an art collector, naming it "The Poker Player", which was hailed by mortals as "a huge step forward in super ugly neorealism."

Percy Jackson and the Olympians: The Lightning Thief (Film)
Percy Jackson cuts Medusa's head off as she is distracted. At Annabeth Chase's suggestion, they take it with them in case it could be used as a weapon. It is wrapped in Grover Underwood's shirt. When not in use, the eyes wear sunglasses to prevent any accidental deaths. It is seen a few times in the story. When collecting one of Persephone's Pearls, Grover uses it to defeat the Hydra. He then kisses it, before reacting in disgust. When the three of them stay at a motel, it is kept in the sink as Grover states that "he cannot pee with her watching him". The trio forgot to close the curtains, and as a consequence, a maid passing by sees it and screams before fleeing. At the end of the story, it is given to Percy's mother and kept in her refrigerator, which again turns Gabe to stone when he breaks open the fridge lock (placed by Percy with a warning message).

Trivia

 * So far both demigods who have cut off Medusa's head have had the same name, though different fathers. Perseus, son of Zeus, and Perseus Jackson, son of Poseidon.