Narfi, Betrayer King — ruling 1

Another snow Zombie creature you control will get only +1/+1 from Narfi's first ability.

Narfi, Betrayer King — ruling 2

Snow is a supertype, not a card type. It has no rules meaning or function by itself, but spells and abilities may refer to it.

Narfi, Betrayer King — ruling 3

The {S} symbol is a generic mana symbol. It represents a cost that can be paid by one mana that was produced by a snow source. That mana can be any color or colorless.

Narfi, Betrayer King — ruling 4

Snow isn't a type of mana. If an effect says you may spend mana as though it were any type, you can't pay for {S} using mana that wasn't produced by a snow source.

Narfi, Betrayer King — ruling 5

Some cards have additional effects for each {S} spent to cast them. You can cast these spells even if you don't spend any snow mana to cast them; their additional effects simply won't do anything.

Narfi, Betrayer King — ruling 6

The Kaldheim set doesn't have any cards with mana costs that include {S}, but some previous sets do. If an effect says such a spell costs {1} less to cast, that reduction doesn't apply to any {S} costs. This is also true for activated abilities that include {S} in their activation costs and effects that reduce those costs.

Narfi, Betrayer King : règles, fonctionnement et interactions (MTG)

Narfi, Betrayer King is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Other snow and Zombie creatures you control get +1/+1. : Return this card from your graveyard to the battlefield tapped. ( can be paid with one mana from a snow source.)

How it works : Narfi, Betrayer King

Original English text — Wizards of the Coast / Scryfall

#1February 5, 2021· Wizards of the Coast
Another snow Zombie creature you control will get only +1/+1 from Narfi's first ability.
No other card is named in this ruling.
#2February 5, 2021· Wizards of the Coast
Snow is a supertype, not a card type. It has no rules meaning or function by itself, but spells and abilities may refer to it.
No other card is named in this ruling.
#3February 5, 2021· Wizards of the Coast
The symbol is a generic mana symbol. It represents a cost that can be paid by one mana that was produced by a snow source. That mana can be any color or colorless.
No other card is named in this ruling.
#4February 5, 2021· Wizards of the Coast
Snow isn't a type of mana. If an effect says you may spend mana as though it were any type, you can't pay for using mana that wasn't produced by a snow source.
No other card is named in this ruling.
#5February 5, 2021· Wizards of the Coast
Some cards have additional effects for each spent to cast them. You can cast these spells even if you don't spend any snow mana to cast them; their additional effects simply won't do anything.
No other card is named in this ruling.
#6February 5, 2021· Wizards of the Coast
The Kaldheim set doesn't have any cards with mana costs that include , but some previous sets do. If an effect says such a spell costs less to cast, that reduction doesn't apply to any costs. This is also true for activated abilities that include in their activation costs and effects that reduce those costs.
No other card is named in this ruling.