Karn, Living Legacy — ruling 1

For Karn’s second loyalty ability, you don’t choose how much mana to pay until the ability resolves. Once the ability begins to resolve and you have paid, no player may respond until you have finished all the steps of that ability.

Karn, Living Legacy — ruling 2

If you don’t pay any mana, you won’t look at any cards or put any into your hand.

Karn, Living Legacy — ruling 3

If you look at one or more cards this way, you must put a card into your hand. You can’t choose not to put one into your hand.

Karn, Living Legacy — ruling 4

Karn’s emblem has an activated ability that allows you to tap untapped artifacts to pay its cost. Notably, you may tap artifact creatures that entered the battlefield this turn to pay this cost, even if they don’t have haste.

Karn, Living Legacy — ruling 5

Powerstone tokens are a new kind of predefined token. Each one has the artifact subtype “Powerstone” and the ability “{T}: Add {C}. This mana can’t be spent to cast a nonartifact spell.”

Karn, Living Legacy — ruling 6

You can use the {C} added by a Powerstone token on anything that isn’t a nonartifact spell. This includes paying costs to activate abilities of both artifact and nonartifact permanents, paying ward costs, and so on.

Karn, Living Legacy — ruling 7

Although all the cards in the Dominaria United set that create Powerstone tokens create a tapped Powerstone token, entering the battlefield tapped isn’t part of the token’s definition. Notably, if you create a token that is a copy of a Powerstone token, the token copy won’t enter the battlefield tapped.

Karn, Living Legacy : règles, fonctionnement et interactions (MTG)

Karn, Living Legacy 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

+1: Create a tapped Powerstone token. (It's an artifact with ": Add . This mana can't be spent to cast a nonartifact spell.") −1: Pay any amount of mana. Look at that many cards from the top of your library, then put one of those cards into your hand and the rest on the bottom of your library in a random order. −7: You get an emblem with "Tap an untapped artifact you control: This emblem deals 1 damage to any target."

How it works : Karn, Living Legacy

Original English text — Wizards of the Coast / Scryfall

#1September 9, 2022· Wizards of the Coast
For Karn’s second loyalty ability, you don’t choose how much mana to pay until the ability resolves. Once the ability begins to resolve and you have paid, no player may respond until you have finished all the steps of that ability.
No other card is named in this ruling.
#2September 9, 2022· Wizards of the Coast
If you don’t pay any mana, you won’t look at any cards or put any into your hand.
No other card is named in this ruling.
#3September 9, 2022· Wizards of the Coast
If you look at one or more cards this way, you must put a card into your hand. You can’t choose not to put one into your hand.
No other card is named in this ruling.
#4September 9, 2022· Wizards of the Coast
Karn’s emblem has an activated ability that allows you to tap untapped artifacts to pay its cost. Notably, you may tap artifact creatures that entered the battlefield this turn to pay this cost, even if they don’t have haste.
No other card is named in this ruling.
#5September 9, 2022· Wizards of the Coast
Powerstone tokens are a new kind of predefined token. Each one has the artifact subtype “Powerstone” and the ability “: Add . This mana can’t be spent to cast a nonartifact spell.”
Card named in this ruling
Powerstone
#6September 9, 2022· Wizards of the Coast
You can use the added by a Powerstone token on anything that isn’t a nonartifact spell. This includes paying costs to activate abilities of both artifact and nonartifact permanents, paying ward costs, and so on.
Card named in this ruling
Powerstone
#7September 9, 2022· Wizards of the Coast
Although all the cards in the Dominaria United set that create Powerstone tokens create a tapped Powerstone token, entering the battlefield tapped isn’t part of the token’s definition. Notably, if you create a token that is a copy of a Powerstone token, the token copy won’t enter the battlefield tapped.
Card named in this ruling
Powerstone