古き道のナーセット
伝説のプレインズウォーカー — ナーセット
+1：あなたは２点のライフを得る。かかを加える。このマナは、クリーチャーでない呪文を唱えるためにのみ使用できる。
-2：カードを１枚引く。その後、あなたはカード１枚を捨ててもよい。あなたがこれにより土地でないカードを１枚捨てたとき、クリーチャー１体かプレインズウォーカー１体を対象とする。古き道のナーセットはそれに、その捨てたカードの点数で見たマナ・コストに等しい点数のダメージを与える。
-6：あなたは「あなたがクリーチャーでない呪文を唱えるたび、クリーチャー１体かプレインズウォーカー１体かプレイヤー１人を対象とする。この紋章はそれに２点のダメージを与える。」を持つ紋章を得る。
Illustrated by
Ikoria: Lair of Behemoths#195MythicJapaneseLegality
Rulings
You can discard a card even if Narset leaves the battlefield before her middle ability resolves. The reflexive triggered ability will still trigger if you discard a nonland card.
If a card you discard has 
in its mana cost, X is considered to be 0.
An ability that triggers when a player casts a spell resolves before the spell that caused it to trigger. It resolves even if that spell is countered.
Because it's a loyalty ability, Narset's first ability isn't a mana ability. It can be activated only any time you could cast a sorcery. It uses the stack and can be responded to.
The emblem created by Narset's last ability is colorless. The damage it deals is from a colorless source.
Narset's second ability goes on the stack without a target. While that ability is resolving, you draw a card and may choose to discard a card. When you discard a nonland card this way, the reflexive triggered ability triggers and you pick a target to be dealt damage. This is different from effects that say "If you do . . ." in that you choose a target after looking at the card you draw and players can respond to the reflexive triggered ability knowing how much damage will be dealt.