+1: You gain 2 life. Add , , or . Spend this mana only to cast a noncreature spell.
−2: Draw a card, then you may discard a card. When you discard a nonland card this way, Narset deals damage equal to that card's mana value to target creature or planeswalker.
−6: You get an emblem with "Whenever you cast a noncreature spell, this emblem deals 2 damage to any target."
Illustrated by Kev Walker · Ikoria: Lair of Behemoths · #278
2020-04-17
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.
2020-04-17
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.
2020-04-17
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.
2020-04-17
If a card you discard has {X} in its mana cost, X is considered to be 0.
2020-04-17
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.
2020-04-17
The emblem created by Narset's last ability is colorless. The damage it deals is from a colorless source.
: Add 
in their mana costs.
. This mana can't be spent to cast a nonartifact spell."