Your focus should be staying alive, taking the focus away from your team, all while lowering their damage and move speed using Alchemical Flask (1), while also immobilizing them using your Binding Word (3). Your Willpower (2) should be used to engage into fights, or used to move faster in the heat of the moment. When max level, your Willpower will have a lot of spirit scaling, and therefore, will give you a lot of barrier when used. Combine this with the resists provided by Last Stand (4), and you will be nigh on unkillable. Better yet, get good gun items, alongside Vampiric Burst or Leech, and your sustain will be incredible. Just make sure you pull back when you get low... you aren't invincible.
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