Gaia Psynergy series

Gaia (ガイア), Mother Gaia (マザーガイア), and Grand Gaia (グランドガイア) are a series of Venus Psynergy featured throughout the Golden Sun series. This Psynergy series is nearly identical to the Rockfall Psynergy series, available to the Samurai class series, to the point of possessing identical visuals prior to Golden Sun: Dark Dawn.

Basic Description
Gaia, Mother Gaia, and Grand Gaia are offensive, ranged Psynergies. The overall power of each stage is determined by comparing the user's Venus Power and the target's Venus Resistance, and multiplying the resultant ratio by the base power of the Psynergy being used.

Visually, each stage of the Gaia series features the ground opening up directly beneath the enemies, followed by a small beam of Venus energy erupting from the opening. The opening will expand and the enemies will then be engulfed by a reverse shower of Venus energy and boulders that emerges. The size of the reverse shower and boulders increases with each successive stage of the series.

Availability
The Gaia series is available to the Squire class series and the Apprentice class series. The Squire class is a mono-elemental Venus class available to Isaac, Felix, and Matthew when they have no or only Venus Djinn Set. More specifically, the series is only available to the stages of Gallant and above, which requires four Venus Djinn to access. The Apprentice class series is a dual-elemental class available to all Venus Adepts, and is accessed by setting Jupiter Djinn. In addition, Jupiter Adepts can access the Enchanter and Conjurer stages of the Apprentice class, via setting Venus Djinn. For all classes, Gaia is learned at Level 7, Mother Gaia at Level 24, and Grand Gaia at Level 54.

Analysis
General: The Gaia series is extremely powerful, with Grand Gaia ranking amongst the most powerful Power-based Psynergies. It is also the latest Psynergy learned, as no character class gains additional Psynergy beyond level 54. For the Squire class, the series is a common endgame Psynergy, alongside Odyssey, due to its power, but can be prohibitively expensive due to the high PP cost. However, the Apprentice class does not have this limit, and thus can make full use of the series. In addition, it is the class's only offensive Venus Psynergy. Another downside is the huge level and power gap between Mother Gaia and Grand Gaia, leaving said Psynergy series outclassed by many offense methods before reaching the rather high level required to learn Grand Gaia.

By Game
Golden Sun: Gaia will only see early game use if Isaac is placed in the Apprentice series; by the time he acquires the four Venus Djinn needed to access it in his base class, it would be outclassed. However, Mother Gaia will likely be the strongest Power-based Psynergy available to Isaac, and thus will see endgame use.

Golden Sun: The Lost Age: Like in Golden Sun, Gaia will likely see little early game use due to the Djinn requirements. Mother Gaia is an excellent Psynergy when exploring the Eastern Sea. Grand Gaia will be learned late in the game, but will be powerful. However, Felix and Isaac will need to watch their PP pools, due to the high PP cost.

Golden Sun: Dark Dawn: The series's role is early role is similar to previous games. However, Grand Gaia is no longer the strongest Power-based Venus Psynergy, with this title going to Reigning Dragon, of the Roaring Dragon Psynergy series. Due to the introduction of the Roaring Dragon series, as well as a mage-style Venus Adept, Himi, who can exploit it, it is possible to allow Matthew to forgo the Gaia series is favor of his stronger Attack-based Psynergies. However, it should be noted that the Grand Gaia is cheaper than Reigning Dragon and has a larger range, allowing for more flexibility.

Trivia

 * The Gaia Psynergy series and the Rockfall Psynergy series are learned at the same levels (except the base one where Rockfall is learned at level 6 while Gaia is learned at level 7). They are also both notable for learning the final stage at level 54, the highest level to learn Psynergy. However, Rockfall is cheaper and weaker.