Mangara's Equity is a uncommon Enchantment card from Mirage (MIR), collector number 26. Current market price: $0.18, TCGplayer market prices via Scryfall.
As this enchantment enters, choose black or red. At the beginning of your upkeep, sacrifice this enchantment unless you pay {1}{W}. Whenever a creature of the chosen color deals damage to you or a white creature you control, this enchantment deals that much damage to that creature.