The Ranger class series is a tri-elemental class series available to the Jupiter Adepts Ivan and Sheba, the Mercury Adepts Mia and Piers, and to a lesser extent, the Mars Adepts Garet and Jenna. Mars and Mercury Djinn are required for the Jupiter Adepts to become this class, while Mars and Jupiter Djinn are required for the Mercury Adepts. The ability to access this class by Mars Adepts is a vastly overlooked quirk in The Lost Age, and requires Mercury and Jupiter Djinn.
This class series's Djinn cadence is similar in structure to the Ninja, Dragoon, and Medium class series. In terms of Psynergy, it mixes together the Jupiter and Mercury Ascetics, sacrificing the Plasma, Prism, and Wish series for the privilege of having three elements of wide-range attack Psynergy available at once.
The class series, when at its highest stage of Warlock and compared to the other series at their highest respective stages, has excellent Agility (tying with the Wizard and surpassed only by the Master) and very high PP, and average HP and Attack, but lower Defense. The series has high Luck. Noteworthy Psynergy from an endgame perspective includes Ward/Resist and Break, and the heaviest area-of-effect Psynergy it has is Pyroclasm. Average stats from an endgame perspective are 155% (162% if you do not factor in Luck).
While the Ranger Class series lacks hard-hitting Psynergy like Prism and Plasma of the White Mage class series, it has access to three different elements worth of Psynergy in Douse, Slash, and Volcano. This can't be said about the other Tri-Elemental classes available to Mercury and Jupiter adepts (the Medium and White Mage classes), giving Rangers a good niche. On top of that, the Ranger's PP pool will tend to last a very long time, since Pyroclasm is the most expensive Psynergy in the set and only costs 29 PP.
The Ranger class series might be one of the best classes (if not the best) for Piers, given that he is more warrior oriented like Isaac and Felix, yet most of his classes are caster oriented like the Hermit and White Mage. From his mono-elemental mariner class, he loses some health, but his defense is a little better and his PP and Agility stats are significantly better, all the while maintaining the same attack and luck.
It should be noted that the Ranger series is the only Tri-elemental class series that has Break, although it is learned later than other classes (34 as opposed to every other class which learns it at 30) and the only Tri-elemental that has Bind.
As a Partial Class
The Ranger class is available to Mars adepts Jenna and Garet with a massive 6 Water or Air and 3 Air or Water Djinn set to them.
Statistically, the 160% PP stat is among the better either can achieve, however, unlike the 150% Attack stat for Ivan and Sheba in the Ninja class, Jenna and Garet have classes which can equal that stat (the Master in the Ninja class) or better it (the War Adept in the Page Class). The same applies for the 160% agility: it can be bested elsewhere and for a far less demanding lineup of Djinn. At the same time, the health, attack and defense statistics ALL leave something to be desired for Jenna and Garet.
Given the high demand of Djinn, weak stats and decent psynergy lineup, the Ranger does not serve as a very good class for Jenna and Garet, and shouldn't be placed high on the priority, even if attempting to utilize the Item Dependents. There exist far better options for partial classes that should be considered (notably the Ninja for Ivan and Sheba, or the Fire or Water Monk in the Pilgrim classes for Garet and Jenna).