Ultimate Skills are very powerful attacks that can be unlocked by successfully filling up the Finesse bar. These attacks level up the more that they are used, like other skills.
Ultimate Skills cost a specific amount of Ultimate to activate, they do not consume Magicka or Stamina. Additional Ultimate can be gained through savvy use of skills in combat and through certain passive skills which increase Ultimate earned.
Ultimate skills are one of the six skills in the hotbar that can be used by players. Some are class based, meaning that different classes will be able to unlock different skills.
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