After a certain number of monsters have been destroyed that are not bosses and do not drop Guardian Acorns, the last one will drop a Piece of Power.
|Number of Heart Containers||Number of Kills|
Every sword slash with a Piece of Power does twice the normal damage and can even send weaker enemies flying across the screen when hit. In addition to the change in sword strength, a Piece of Power also increases Link's movement speed.
The strength effect of the Piece of Power does stack with the Red Clothes and the L2 Sword. The effect fades after Link is hit by enemies 3 times, after moving through some loading zones, after a Save+Quit, or after Link dies. For an exact list of damage output check the page about Damage Values and Weapon Strength. Falling into hazards like Lava and Pits will not count towards the 3 hits.