From Golden Sun Universe

Mythril Silver is advanced forgeable material in Golden Sun: The Lost Age. It is described as "Legendary dwarven metal" (this solidifies the apparent fact that the residents of Loho, where one piece of Mythril Silver can be found, are a race of dwarves). It is found in various areas after the Wings of Anemos are acquired, such as in Loho, and it can also be dropped very rarely from a Soul Army in Yampi Desert Cave (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 2000 coins and sold for 1500 coins. It can be forged into the following highly powerful equipment:

Levatine: Long Sword class: Attack +173: Unleashes Radiant Fire, which converts to Mars damage, adds 66 attack points, and can lower the target’s defense down to 50%. It is bought for 19700 coins and sold for 14775 coins. The chance of it being forged is 10%.
Mythril Armlet: Bracelet class: Defense +46: Raises Critical Hit and Unleash rate by 10%. It is bought for 9700 coins and sold for 7275 coins. The chance of it being forged is 20%.
Mythril Blade: Long Sword class: Attack +160: Unleashes Lethe Albion, which converts to Mercury damage, adds 56 attack points, and can seal the target’s Psynergy. It is bought for 14600 coins and sold for 10950 coins. The chance of it being forged is 20%.
Mythril Clothes: Clothing class: Defense +49: Raises Critical Hit and Unleash rate by 15%. It is bought for 14900 coins and sold for 11175 coins. The chance of it being forged is 20%.
Mythril Helm: Helm class: Defense +44: Raises Critical Hit and Unleash rate by 12%. It is bought for 11400 coins and sold for 8550 coins. The chance of it being forged is 15%.
Psychic Circlet: Circlet class: Defense +39: PP recovery +12. It is bought for 8800 coins and sold for 6600 coins. The chance of it being forged is 15%.

[edit] Analysis

Several pieces of the Mythril Silver-forged equipment are among the best equipment in the game. The Mythril Clothes are a slightly-toned down Valkyrie Mail, but it can be worn by any Adept, the Mythril Helm is an ideal piece of headwear for offensive warrior Adepts, and the Psychic Circlet has a very high PP recovery rate (sure to be useful to any Psynergy-centered Adept). However, the Levatine can be outperformed by weapons with unleashes that multiply attack power, and the Mythril Armlet is ultimately an inferior form of the Riot Gloves.

[edit] RNG Method

Here is the RNG method for how to get Mythril Silver.

Mythril Silver Dropped by Soul Armies in the Yampi Desert Cave. Standard rules apply.

Attack order: Felix, Jenna, Sheba, Piers

Round 1

Felix casts Quake. Big arrow: Soul Army

Jenna casts Beam. Big arrow: Soul Army

Sheba casts Whirlwind. Big arrow: Other Enemy

Piers casts Tundra. Big arrow: Other Enemy

Round 2

Felix casts Quake. Big arrow: Soul Army

Jenna casts Beam. Big arrow: Soul Army

Sheba unleashes Whorl. Soul Army dies.

Piers attacks the other enemy. Other enemy dies.

You got some Mythril Silver.

Forgeable Items in Golden Sun: The Lost Age
Tear Stone • Star Dust • Sylph Feather • Dragon Skin • Salamander Tail • Golem Core • Mythril Silver • Dark Matter • Orihalcon List of Rusty items