Stamata Revithi's Document

Origin
Stamata Revithi was a Greek woman who ran the 40-kilometer marathon at the 1896 Olympics. Although the games excluded women from participating, she ran after the men left for five and a half hours. She found witnesses to sign a document saying she completed the race, but was barred from entering Panathinaiko Stadium. She planned on submitting it to the Olympics committee, but the signed document verifying her feat that went unverified by the committee.

Effects
When held, it allows the user to accomplish astounding feats of physical and mental nature, though if not directly witnessed then no one will believe it happened.