Not sure what you mean exactly, but the 'Sword on Fire' is any Sword that has the ability to inflict 'Fire' on an enemy via a Critical Hit I believe. It's the same with any element, Poison, Curse, Fire or Frost - if the Critical Hit (or Melee/any attack?) has the ability to inflict an element, the Sword will reflect this (e.g look 'frosty if Frost is the element, look 'poisony' if Poison is the element, look 'cursed' if Curse is the element. You 'upgrade' them by meeting their Gear Challenge, and once the July update is out you can level them up to your current level (with Myrian) if their Gear Challenge has been met.
Thursday - last edited Thursday
Are you talking about this sword?
It's called the Sword of War, and the upgrade challenge on any piece of gear is written on it in the inventory menu. In this particular case, you have to recruit an enemy Captain/Warchief/Overlord of a specific level from the Warmonger tribe.
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