The Legend of Zelda: a Link to the Past Walkthrough Part 22

Link fights the seventh boss of the Dark World: Trinexx. Use the Fire Rod on the ice head. And the Ice Rod on the fire head. After it he will turn into a snake and you just need to unleash your sword at his shining tail.

Link gets the last Crystal Maiden.

ITEMS FOUND:
Silver Shield Lv 3
Piece of Heart
Seventh Crystal Maiden