Thornscape Familiar
Creature — Insect
Red spells and white spells you cast cost less to cast.
Blessed with many options, Thornscape masters favor scarabs as familiars.
Illustrated by
Planeshift#95CommonEnglishLegality
Rulings
This can lower the cost to zero, but not below zero.
The effect is cumulative.
The lower cost is not optional like with some other cost reducers.
Can never affect the colored part of the cost.
If a spell is both red and white, you pay less, not 
less.
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.
If this card is sacrificed to pay part of a spell’s cost, the cost reduction still applies.