UNDOCUMENTED MECHANICS
Fire Mastery raises your own fire damage across the board — it is not a bonus for your minions. Skills in this class that benefit: Fire Bolt, Inferno, Blaze, Fire Ball, Fire Wall, Enchant, Meteor, Hydra. Their listed damage figures already include Fire Mastery — every point in it moves those numbers. The game does not list Fire Mastery under their “Receives Bonuses From”, so the connection is invisible on the skill pages.