Sympathetic Substance

Achilles Heel: Sympathetic Substance by Senator Cybus

The Mega Hero has a peculiar effect on one particular substance (a precious metal, type of gem, etc.) - it glows in his presence! Whenever the hero gets within 20 feet (6 m) of the substance, it will glow like a candle, its light getting slightly (but noticeably) brighter the closer he gets.
No matter how he might try to conceal or disguise himself, the hero cannot prevent this reaction, giving knowledgeable enemies the perfect advance warning of his approach.
In the interests of fairness, GM's and players should choose the substance together - gold, Kisentite and diamonds are reasonable choices, whereas oxygen or Sasquatch sweat are not.