Theory[]
I believe that the animated series gives a clue as to the new rule regarding Mana.
In the series, each Duelist seems to specialize in at least one Civilization: e.g. Ray & Fire/Nature, Gabe & Water, Allie & Darkness, Nigel & Light, etc. However, we've seen Duelists use Creatures outside of the Civilization that they specialize in. Chimera-gui 02:29, June 28, 2012 (UTC)