Coal

Location
Coal is acquired in a cutscene in Izumo. You first have to have completed the Gaia Rock dungeon, including defeating the Serpent, then triggered a lengthy story cutscene in Izumo with Lady Uzume, Susa, and Kushinada. Following that, you may present the Dancing Idol key item that you had found and made use of in Gaia Rock to Uzume, and through another cutscene she exchanges Coal - a pet that has apparently become very dear to her - for the dancing doll of Mt. Mikage.

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

When Coal's battle effect is used, all currently active and alive Adepts get their Agility ratings temporarily buffed to +100%, the maximum agility bonus possible. It doubles everyone's speed, in other words. The previous game's Jupiter Djinni Zephyr has the exact same effect.

Ability analysis
In The Lost Age up until Isaac's party joins along with their returning Djinn late in the game, Coal is the only effect that increases agility in any way, and is the one Djinni that doubles everyone's speed. This makes it very useful, perhaps life-saving, to use all throughout the game, particularly against bosses, allowing you several turns where your party can safely attack and heal themselves before the enemy gets to take its action(s) those turns. Isaac's party brings with them the Jupiter Djinni Zephyr, which has the same effect, and the two continue to be extremely practical interchangeably if the player decides to use them specifically during boss fights where the boss happens to be faster than several Adepts and that proves to be a problem.

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

The manual to the North American version of The Lost Age incorrectly names this Djinni "Turbo".