Dwarven Swordsmith

The are twin characters in.

In the Light World, the smiths can be found to the southeast of Kakariko Village. One of the smiths remarks that he can only temper Link's sword when his partner returns.

In the Dark World, the missing Dwarven Swordsmith can be found just south of the Village of Outcasts near the Digging Game. He is in a frog-like form, due to the Dark World's magic, and is surrounded by black stones which can only be lifted with the Titan's Mitt.

Link can then use his Magic Mirror to transport both him and the smith back to the Light World, and reunite the two Dwarves. As a reward, they will offer to temper Link's Master Sword into a Tempered Sword.