- This article is about the element. For the Summon sequence, see Mercury (summon).
The element of Mercury is represented by fish, who are said to rule the seas. Mercury-based Psynergy typically invokes water and/or ice in offensive attacks. Certain puzzles in the Belinsk Ruins invoke the element of Mercury via the Douse Psynergy, a basic Psynergy that summons a small rainshower.
In a few instances throughout the series, Mercury's relationship with the other elements is demonstrated or implied. In Golden Sun, the release of Mercury Psynergy from Mercury Lighthouse is specifically stated to have weakened the Mars Adept, Saturos, to the point that Isaac's party was able to defeat him in battle. Mars's weakness against Mercury would lead Karst and Agatio to target the Mercury Adept Mia, in an attempt to prevent her from being able to use her Psynergy against them. However, Mercury's more symbiotic relationship with Jupiter is more implied than stated outright. In The Lost Age, it is theorized that the combined power of Mercury and Jupiter is what caused temperatures worldwide to plunge.
Most offensive Mercury Psynergies are Power-based, with the Cutting Edge series and the Diamond Dust series making up the only Attack-based offenses. The Mercury element has many Utility Psynergies associated with it, including the Douse, Frost, Cold Snap, Cloak, Lift, and Parch.
One major aspect of the Mercury element lies in its extensive healing capabilities, which form the bulk of the element's Support Psynergy. While all four elements have healing capabilities to some extent, Mercury-based heals are the strongest. The Ply Psynergy series contains the strongest single-target heal, while the Wish Psynergy series contains the strongest mass-healing move. Also included in the healing arsenal is Cure Poison and Restore, moves that allow players to remove almost any status condition.
 Adepts of the Mercury Element
Nearly all known Mercury Adepts come from either Imil or Lemuria. Mercury Adepts from Imil are descendents of the Mercury Clan, a clan charged with watching over Mercury Lighthouse, which serves as the source of their powers. While nearly every Lemurian is a Mercury Adept to some degree, their is no known source for their powers. Unlike the other elemental rocks, Aqua Rock, an area of potent Mercury Psynergy, seems to have no associated population of Adepts. While there is a community nearby, the Apojii Islands, who is aware of Aqua Rock, no one has demonstrated Mercury-based abilities. By the time of Dark Dawn, at least one other Mercury Adept, Amiti, exists in Ayuthay; it is mentioned that he inherited his powers from his father, a powerful, but unknown Mercury Adept.
Most Mercury Adepts seem to have the shared trait of possessing blue hair. It is also interesting to note that all playable Mercury Adepts have a small lock of hair that stands up. Alex has this distinction as well. In line with the elements capabilities, Mercury Adepts that join the player's party possess powerful healing Psynergy, and most have been seen using this power in cutscenes. Mia in particular is known in Imil for her extensive healing capabilities. However, there are those, such as Piers and Amiti, who forego learning the more advanced recuperative abilities for more offense-oriented Psynergies.