Ninja class series

The Ninja class series is a tri-elemental class series available to the Venus Adepts Felix and Isaac, the Mars Adepts Garet and Jenna, and to a limited extent, the Jupiter Adepts Ivan and Sheba. 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 found only in The Lost Age.

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 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, although 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.

In the original Golden Sun if every single Djinni has been collected up to Colosso Finals, then Isaac can be into a Ninja, which is an excellent class for him to be in for that event. 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.

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.