Img Source: Trion Worlds

The Arbiter is the Patch 2.7 Soul for Mages. It is a Tank soul that uses Water and Air-based abilities with magical damage mitigation to tank.

Obtained: “Dream Soul Pack” from Rift Store -> Services for 5,000 Credits (4,500 for Patrons). The Dream Soul Pack provides you with the Liberator, Physician, Arbiter and Oracle souls, applied account-wide.

Lore

The Arbiter, Voradrin, is a Runemaster dwarf who is also the librarian and protector of an out-of-the-way library known as the Runic Athenaeum.

It is unknown whether he comes from an alternate reality as he is present (on the PTS) in the Runic Athenaeum; although he does seem to belong to a different time period (the past).

He studied a variety of books and scrolls given to him by Bahralt – allowing him to lead a path that was different from his other Mage brethren – one that uses magic to protect.

You can still find and interact with him in the Runic Athenaeum in Moonshade Highlands where he will provide you with various soul- and lore-based quests.

More information about the lore of the Arbiter can be found on the RIFT website here.

Soul Abilities

The new Mage soul – Arbiter – is a Tanking soul that uses ice shields, magical mitigation spells and taunts with storm-based abilities.

• Magelo has a Soul tree builder for the Arbiter soul (and other 2.7 souls) here.
• A list of Soul Abilities can be found at Magelo.

Guides

There are guides available that may assist you in playing the Arbiter spec, listed below:

• Ianto Jones: An Introduction to Magetank (61 Arbiter)
  Very detailed guide on 61 Arbiter. 61 Arb/10 Warlock/5 Storm; 61 Arb/10 Harb/ 5 Storm + other utility builds.
  
• Burninalways: Quick Arbiter Guide
  Various Arbiter Specs with a standard rotation, macros and ability breakdown.

Links

• RIFT: “The Arbiter” Lore post.
• Magelo: PTS Soul Tree Calculator
• Magelo: Arbiter Soul Abilities
• Guide: Accessing the PTS + Dummy Foundry

Also check out the other Patch 2.7 souls: