Margomill is the boss of the House of Gales, a large, multi-eyed creature that spins rapidly. The battle takes place on a circular platform with strong wind currents. The key to defeating Margomill is to use the Hookshot. In its first phase, Margomill will spin around, occasionally stopping to reveal its eye. When it stops, use the Hookshot to pull yourself towards its eye, then quickly slash it with your sword.
As you damage it, Margomill will shed layers, becoming smaller and faster. The wind currents will also become more erratic. Continue to use the Hookshot to close the distance to its eye and attack. Be careful not to get knocked off the platform by the wind or by Margomill's spinning attacks. In its final phase, it will be very small and fast, requiring precise timing with your Hookshot. Defeat it to rescue Rosso and obtain the Pendant of Wisdom.