Coal

Coal is a Mars Djinni found in Golden Sun: The Lost Age, and is numerically the twelfth Mars Djinni found overall and the fifth found in The Lost Age.

Location
Coal is acquired as a reward from Lady Uzume in Izumo after defeating the Serpent and giving her the Dancing Idol found and used in Gaia Rock.

Description
When Set, it increases base HP by 11, base PP by 3, and base Agility by 3.

When used, Coal increases the agility ratings of all party members to double the base amount.

Analysis
Coal doesn't seem to be of much use in the game, most likely because on average the player's party will normally be faster than any standard enemy. Though it can be of some help in Boss battles as most bosses have a high Agility rating.

Name Origin
Coal is a readily combustible black rock used to start small fires.