Hero's Charm

From Zelda Wiki.org

The Hero's Charm is a golden Mask in The Wind Waker that enables the player to see the life energy for enemies when equipped. It is worn on the face, and the life energy appears as a green bar next to the enemy when it is L-Targeted. It is obtained after giving Miss Marie 40 Joy Pendants.

In boss fights, excluding Ganondorf, the energy is displayed at the bottom of the screen.

Trivia

The two eyes on the mask resemble the Sheikah eye symbol.