Zaffai, Thunder Conductor — ruling 1

"That spell's mana value" refers to the spell that caused the ability to trigger, not the card you look at when you scry.

Zaffai, Thunder Conductor — ruling 2

If the instant or sorcery spell has {X} in its mana cost, X is the value chosen for X as the spell was cast.

Zaffai, Thunder Conductor — ruling 3

The wrong card name was inadvertently included in Zaffai's printed rules text. The text above is correct and the full name of the card is Zaffai, Thunder Conductor.

Zaffai, Thunder Conductor — ruling 4

Each magecraft ability has a different effect, although they all have the same trigger condition, whenever you cast or copy an instant or sorcery spell.

Zaffai, Thunder Conductor — ruling 5

For example, if you control Archmage Emeritus and cast an instant or sorcery spell, Archmage Emeritus's magecraft ability will trigger and you will draw a card.

Zaffai, Thunder Conductor — ruling 6

If an effect creates a copy of an instant or sorcery spell, this will also cause the magecraft ability to trigger.

Zaffai, Thunder Conductor — ruling 7

If an effect creates multiple copies of an instant or sorcery spell, magecraft abilities trigger once for each copy created by the effect.

Zaffai, Thunder Conductor — ruling 8

Some effects instruct you to copy an instant or sorcery card in a zone other than the stack. These copies do not cause magecraft abilities to trigger. However, most effects that do this also allow you to cast the copy, and casting the copy will cause magecraft abilities to trigger.

Zaffai, Thunder Conductor : règles, fonctionnement et interactions (MTG)

Zaffai, Thunder Conductor 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

Magecraft — Whenever you cast or copy an instant or sorcery spell, scry 1. If that spell's mana value is 5 or greater, create a 4/4 blue and red Elemental creature token. If that spell's mana value is 10 or greater, Zaffai deals 10 damage to an opponent chosen at random.

How it works : Zaffai, Thunder Conductor

Original English text — Wizards of the Coast / Scryfall

#1April 16, 2021· Wizards of the Coast
"That spell's mana value" refers to the spell that caused the ability to trigger, not the card you look at when you scry.
No other card is named in this ruling.
#2April 16, 2021· Wizards of the Coast
If the instant or sorcery spell has in its mana cost, X is the value chosen for X as the spell was cast.
No other card is named in this ruling.
#3April 16, 2021· Wizards of the Coast
The wrong card name was inadvertently included in Zaffai's printed rules text. The text above is correct and the full name of the card is Zaffai, Thunder Conductor.
No other card is named in this ruling.
#4April 16, 2021· Wizards of the Coast
Each magecraft ability has a different effect, although they all have the same trigger condition, whenever you cast or copy an instant or sorcery spell.
No other card is named in this ruling.
#5April 16, 2021· Wizards of the Coast
For example, if you control Archmage Emeritus and cast an instant or sorcery spell, Archmage Emeritus's magecraft ability will trigger and you will draw a card.
No other card is named in this ruling.
#6April 16, 2021· Wizards of the Coast
If an effect creates a copy of an instant or sorcery spell, this will also cause the magecraft ability to trigger.
No other card is named in this ruling.
#7April 16, 2021· Wizards of the Coast
If an effect creates multiple copies of an instant or sorcery spell, magecraft abilities trigger once for each copy created by the effect.
No other card is named in this ruling.
#8April 16, 2021· Wizards of the Coast
Some effects instruct you to copy an instant or sorcery card in a zone other than the stack. These copies do not cause magecraft abilities to trigger. However, most effects that do this also allow you to cast the copy, and casting the copy will cause magecraft abilities to trigger.
No other card is named in this ruling.