Piece of Power

Pieces of Power, also known as Piece o' Power, are triangular-shaped items that appear in The Legend of Zelda: Link's Awakening, The Legend of Zelda: Link's Awakening DX, and the Nintendo Switch remake. They sometimes appear when Link defeats an enemy. When Link picks up a Piece of Power, his sword begins to flash (both on-screen and on the bottom HUD), and a unique theme plays while it is in effect. A Piece of Power enables the sword to deal twice as much damage to enemies, sending them flying in the process. It also enables Link to move around faster. In the reissues, if Link is wearing the Red Clothes, the effect of a Piece of Power will stack and enable him to do four times the damage than usual.

The Piece of Power's effect wears off if Link takes damage three times (except for when he falls into a pit or lava), or by switching between locations from a dungeon, cave, or the overworld.

Guardian Acorns are similar items to Pieces of Power in that the same theme plays while they are in effect. The difference is that Guardian Acorns increase Link's defense rather than his sword attack.

Trivia

 * In The Legend of Zelda: Link's Awakening review of the Australian Nintendo Magazine System's tenth issue, the Pieces of Power are said to be fragments of the Triforce (parsed Tri-Force in the magazine).