Black creature spells you cast cost less to cast.
Whenever you cast a creature spell, each opponent loses 1 life and you gain 1 life.
Jonas De Ro
To determine the total cost of a creature spell, start with the mana cost or alternative cost youâ€™re paying, add any cost increases, then apply any cost reductions. The converted mana cost of the creature remains unchanged, no matter what the total cost to cast it was.
In a Two-Headed Giant game, the triggered ability of Bontuâ€™s Monument causes the opposing team to lose 2 life and you gain 1 life.
Each Monumentâ€™s triggered ability triggers as the creature spell is cast and resolves before that creature spell resolves. The ability will resolve even if that creature spell is countered.
Each Monument has one ability that reduces the cost of creature spells of a certain color, and a triggered ability that triggers whenever you cast any creature spellâ€”not just a creature spell of that color.
A creature spell thatâ€™s multiple colors is each of those colors. For example, Ahn-Crop Champion is a white creature and a green creature, so it can benefit from either Oketraâ€™s Monument or Rhonasâ€™s Monumentâ€”or both at once.