Sylph Feather

A Sylph Feather is a piece of forgeable material in Golden Sun: The Lost Age. It is described as a "Wind essence feather". It is found in various areas after the Lemurian Ship is acquired, such as in Tundaria Tower, and it can also be dropped rarely from a Great Seagull in Treasure Isle (fell it with Jupiter Djinn to increase drop rate by four times). Being an Artifact, it can be sold and later repurchased. It can be bought for 700 coins and sold for 525 coins. It can be forged into the following moderately powerful items, all Jupiter-based:

Aerial Gloves: Glove class: Defense +37: Agility +30: Jupiter power +20. It is bought for 5400 coins and sold for 4050 coins. The chance of it being forged is 25%. Faery Vest: Clothing class: Defense +38: Use to restore 200 HP to an ally. It is bought for 6900 coins and sold for 5175 coins. The chance of it being forged is 25%. Floating Hat: Hat class: Defense +34: Jupiter resistance +20: Luck x1.2. It is bought for 5700 coins and sold for 4275 coins. The chance of it being forged is 25%. Sylph Rapier: Light Blade class: Attack +124: Unleashes Mad Zephyr, which converts to Jupiter damage, adds 40 base attack, and sometimes attacks for twice as much damage. It is bought for 10400 coins and sold for 7575 coins. The chance of it being forged is 25%.

Locations

 * Tundaria Tower Claimable once the player acquires the Burst Brooch.
 * Treasure Isle Claimable once the player acquires the Grind Stone.
 * Ankohl Ruins Claimable once the player acquires the Sand Psynergy.

Analysis
Sylph Feather-crafted equipment is generally most useful as soon as you have it forged following grabbing the individual Sylph Feathers in Tundaria Tower and Ankohl Ruins.