Ninja class series

The Ninja class series is a tri-elemental class series available to the Venus Adepts, the Mars Adepts and to a limited extent, the Jupiter Adepts. The Venus Adepts will be under the influence of this series if they have both Jupiter and Mars Djinn set to them; similarly, the Mars Adepts become this class when they have Jupiter and Venus Djinn set to them. The Jupiter Adepts can only access the Ninja class, and require Venus and Mars Djinn to be set to them. The access to this class series by the Jupiter Adepts is a vastly overlooked quirk to the Ninja class not found in Golden Sun.

This class series's Djinn cadence is very similar to the Dragoon, Ranger, and Medium class series in structure. Unlike these other classes, the Ninja does not combine together the two variations of another class (in this case, the source would have been the Venus and Mars Enchanters), but has a unique variety of Psynergy. Whereas the Enchanters seem to specialize in status abilities, all of the Ninja's Psynergy except Mist is some sort of attack.

The class series, when at its highest stage of Master and compared to the other series at their highest respective stages, has unsurpassed Agility that is the highest Agility rating of any class, superb Attack tying with the Chaos Lord for highest Attack rating, excellent HP tying with the Paladin and Chaos Lord and surpassed only by the Ronin, and even above average PP, but with lower Defense. The series has low Luck tying with the Beast Lord and being above only the Chaos Lord. Noteworthy Psynergy from an endgame perspective includes Annihilation, Death Leap, and Shuriken, and the heaviest area-of-effect Psynergy it has are Thunderhead and Punji Strike. Average stats from an endgame perspective are 157% (172% if you don't factor in Luck).

Analysis
Any Ninja in the lineup is almost always going to be taking his or her turn first, and probably only bested by another Ninja in the lineup with a superior baseline agility (Jenna vs. Garet).

Boasting three elements worth of hard-hitting, offensive damage dealing Psynergy and a good PP to run with it, the Ninja is one of the best classes for bringing down multiple enemies. Although the Ninja has zero beneficial (buffing) psynergy series, Gale does function like Whirlwind in terms of a utility Psynergy (which is nice as you are probably taking Whirlwind away from Sheba and/or Ivan to make somebody a Ninja).

When it comes to Master or Ronin, the decision, like everything else when it comes to the classes, is the player's individual preferences, desires and goals, although the Ninja has better multi-target Psynergies than the Samurai, while the Samurai has better single target ones.

In the original Golden Sun if every single Djinni has been collected up to Colosso Finals, then Isaac can be set into a Ninja, which is an excellent class for him to be in for that event. Death Plunge will make quick work of the other combatants, and the attack stat is decent enough to still do good damage. Make sure you try and get some of the nuts just to be on the safe side. Since you'll trading Earth Djinn to Ivan, Ivan will learn Growth at that point which frees up Garet to do any Moving necessary for the finals.

The Ninja Class may be one of the best classes (if not the best) for Jenna (barring high level four Ronin runs) given that she is more "caster" oriented yet has many of the "warrior" classes like the Brute or Samurai (Himi faces a similar issue, though has access to the Curse Mage class series). From her mono-elemental Flame User class, she gains a lot of attack, health and agility, while maintaining the same defense and psynergy points at the cost of 10% of her luck. Her natural PP growth is higher than any of the other adepts who can utilize this class (not including Ivan and Sheba who can get this class partially) and her ability to use light blades will allow her to capitalize pretty well on all aspects of the class.

As a Partial Class
The Ninja class is available to Jupiter adepts Ivan and Sheba in the later parts of the game for a massive 6 Earth or Fire Djinn and 3 Fire or Earth Djinn.

Statistically, the 150% attack is the best either adept can hope to achieve and the 170% agility is on par with the Sorcerer, the top level of their mono-elemental class. At the same time, the 140% PP stat won't seem too bad with their natural PP stat (Ivan and Sheba hold the best and second best natural PP stats respectively).

Compared to other partial classes, the Ninja serves as one of the better choices, all things considered, especially for Ivan who can capitalize on the above average attack stat better with Light Blades. However, the staggering djinn cost, combined with the frailty of the setup (one Djinni set to Stand by will immediately knock them out of the class) must be taken note of. If you are attempting to utilize Item Dependent classes however, than the Ninja might help you to better capitalize and utilize your Djinn better if considered.

Trivia

 * In Golden Sun, Thunderhead was called Thunderstorm. However, that name caused problems with fitting text into single lines, so it was changed to the shorter Thunderhead for The Lost Age.