Curse of Achilles

The Curse of Achilles is a power that a person can acquire when they bathe in the River Styx.

Description
The curse is named after Achilles, the Ancient Greek hero, who was famous for his invulnerability. When one bathes in the Styx, they will granted the power to remain uninjured by any means. They must get their parent's blessing. When one bathes in it, the person must envision one thing that ties them to the living. They also must imagine a single spot on their body with a rope tying them to the mortal plane. If they do not do this they will turn into ash and be forever lost in the Styx. Though not proven, the thing a person usually envisions is often someone close.

Weakness
The most obvious weakness is the mortal spot the person chooses, as it remains the only place that can be injured. Should this spot be injured, the person will die immediatly.

The less obvious weakness is a secondary function - in addition to gaining invulnerability, someone with the Curse of Achilles also gains extreme physical prowess - heightened strength and reflexes - and a body that almost automatically fights. However, this places an enormous amount of stress on the body, requiring a warrior under the Curse to be careful not to over-exert himself, which happens more quickly than before. Chiron said that Achilles himself took about twenty naps a day--it sometimes seemed that when Achilles wasn't fighting, he was either sleeping or eating. This means someone under the Curse will tire fighting normally than someone who isn't - meaning they could be neutralized by being put in a position where they must fight, and making sure their enemies are expendable.