Ragemonger is a uncommon Creature — Minotaur Shaman card from Born of the Gods (BNG), collector number 153. Current market price: $0.22 (foil $0.53), TCGplayer market prices via Scryfall.
Minotaur spells you cast cost {B}{R} 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 {2}{R}, it costs {2} to cast.)