2004-10-04 : Can never affect the colored part of the cost.

2004-10-04 : If a spell is both black and green, you pay {1} less, not {2} less.

2004-10-04 : If this card is sacrificed to pay part of a spell’s cost, the cost reduction still applies.

2004-10-04 : The effect is cumulative.

2004-10-04 : The generic X cost is still considered generic even if there is a requirement that a specific color be used for it. For example, “only black mana can be spent this way”. This distinction is important for effects which reduce the generic portion of a spell’s cost.

2004-10-04 : The lower cost is not optional like with some other cost reducers.

2004-10-04 : This can lower the cost to zero, but not below zero.