Mariner class series

The Mariner Class series is the default class series available to the Mercury Adept Piers, ands he is under the influence of these classes if he either has Mercury Djinn or no Djinn set onto him. The Water Seer Class series is unique only to Piers; As he is a warrior and Mia, the other Mercury Adept, is a mage, she has a different Mercury-based class series unique to her as well, the Water Seer Class series.

Statistical Influence
Mariner (0-1 Mercury Djinn): (Percentages about how all stats are affected go here).

Privateer (2-3 Mercury Djinn):

Commander (4-5 Mercury Djinn):

Captain (6-7 Mercury Djinn):

Admiral (8-9 Mercury Djinn):

Psynergy Setup
The Mariner class begins with the Diamond Dust Psynergy Technique, the Frost Psynergy series, the Cool Psynergy series, the Ply Psynergy series, and the Cure Poison, Restore, and Break Psynergies. In the Privateer class (the class Piers is actually in when he first joins your party, as he carries two Mercury Djinn with him), the Avoid Psynergy is gained. The Commander class retains this Psynergy setup, and in the Captain Class, Diamond Dust is upgraded into the Diamond Berg Psynergy Technique. The Admiral class retains this Psynergy setup.

It is widely argued that the Mariner Class series is better for battle than the Water Seer Class series, while the latter is better at healing.