Appearance and Mechanics Edit
Moon Essence is a liquid kept in a moon-shaped bottle. What it is, exactly, is unknown - but it does have magical properties. In Hansel and Gretel, giving the bottle of Moon Essence to an imp under the Evil Witch's control frees him from her command. How or why it does this is left unknown.
Moon Essence is used in The Red Riding Hood Sisters to bind together the Moonstones. The Wolf Queen wishes to do this in order to plunge the world into eternal night. According to the will of the person brandishing the Moon Essence, it can either bind together the Moonstones or destroy them entirely.
When the Moon Goddess was imprisoned by the Evil Witch, a bottle of Moon Essence was also locked in a stand beside the statue holding the Goddess. Hansel unlocks this stand and obtains the bottle, which he gives to an imp that is being commanded by the Evil Witch. Now free, the imp flies off.
At this point in the Moon Essence's history, we don't know what happened to it. At some point, it came into the possession of the Red Riding Hood Sisters. They kept it hidden inside a shrine dedicated to the Moon Goddess. Only the Elder Sister of the Sisterhood was allowed to access the shrine.
When the Elder Sister, Teresa, was killed by the Wolf Queen, the remaining Sisters and the Fairytale Detective entered the shrine and found the hidden Moon Essence. They intended to use it to destroy the Moonstones and prevent the Wolf Queen from bringing eternal night to the world. However, they were tricked and the Essence ended up in the Wolf Queen's paws, anyhow.
The Moon Essence was used to bind the Moonstones, but before the entire process was completed, a Moonstone was destroyed by Raphael. The resulting reaction caused the entire Fabled Land around them to be destroyed.
It is assumed that the Moon Essence was destroyed along with the Fabled Land.