Master Mode

is a mode in included in  DLC Pack.

Overview
In Master Mode, most enemies and bosses are powered up by one level, can detect Link's approach easier and regain health over time; however, there is a limit to their health recovery. Stronger, golden versions of enemies are also introduced. Some enemies, such as Lynels, also appear in more areas, including the Great Plateau. Enemies and Treasure Chests may also appear floating in the sky on planks being held by Sky Octoroks, usually containing strong and rare weapons such as the Royal Guard set.

There is ordinarily a mechanism preventing Link from getting killed in one hit by powerful attacks, leaving him alive with a quarter Heart instead. This protection is not present in Master Mode.

While playing Master Mode, a small Triforce will appear on the bottom left of the screen. Save data for Master Mode is kept separately from Normal Mode. In contrast to Normal Mode, there is only one Autosave slot available.

Trivia

 * The Master Mode was originally called Hard Mode during the Expansion Pass announcement.