Oracle Text

Minotaur spells you cast cost BR less to cast. This effect reduces only the amount of colored mana you pay. (For example, if you cast a Minotaur spell with mana cost 2R, it costs 2 to cast.)

Card Rulings

2/1/2014 If you control more than one Ragemonger, the cost reduction is cumulative.
2/1/2014 You apply cost reduction effects after other cost modifiers, so Ragemonger can reduce additional costs or alternative costs of Minotaur spells if they include and/or .
2/1/2014 If a spell has hybrid mana symbols in its mana cost, you choose which half you will be paying before determining the total cost. If you choose to pay such a cost with or , Ragemonger can reduce that part of the cost.