ギルドパクトの印章
アーティファクト
ギルドパクトの印章が戦場に出るに際し、色２色を選ぶ。
あなたが呪文を唱えるためのコストは、その選ばれた色のうちその呪文の色である色１色につき
少なくなる。
「私はギルド同士が剣を持って街路で争うより、政権の場で言葉を尽くして論争することを望む。」 ――ジェイス・ベレレン
Illustrated by
Ravnica Remastered#266RareJapaneseLegality
Rulings
You must choose two different colors.
Seal of the Guildpact’s last ability doesn’t change the mana cost or converted mana cost of any spell. It changes only the total cost you pay.
Seal of the Guildpact’s last ability can’t reduce the amount of colored mana you pay for a spell. It reduces only the generic component of that cost.
If there are additional costs to cast a spell, or if the cost to cast a spell is increased by an effect (such as the one created by Thalia, Guardian of Thraben’s ability), apply those increases before applying cost reductions.
The cost reduction can apply to alternative costs such as evoke costs.
If a spell you cast has 
in its mana cost, you choose the value of X before calculating the spell’s total cost. For example, if that spell’s mana cost is 
and you’ve chosen red and green, you could choose 5 as the value of X and pay 
to cast the spell.