Tetzin, Gnome Champion // The Golden-Gear Colossus — ruling 1

You can target any double-faced artifact you control with The Golden-Gear Colossus's triggered ability, but only transforming double-faced cards and transforming tokens can transform. Choosing an artifact represented by a modal double-faced card (Pestilent Cauldron from Strixhaven, for example) won't cause that permanent to transform.

Tetzin, Gnome Champion // The Golden-Gear Colossus — ruling 2

The back faces of some cards with craft refer to cards "used to craft" it. This refers to the cards exiled as part of the cost of the craft ability of the front face. Those cards are considered to be "used to craft" that permanent as long as they remain exiled and the permanent remains on the battlefield, even if the permanent's controller changes or some of its characteristics change (because of a copy effect, for example.)

Tetzin, Gnome Champion // The Golden-Gear Colossus — ruling 3

If the materials required include multiple objects, you may exile some of them from among permanents you control and the rest from among cards in your graveyard. You don't have to choose all permanents or all cards from your graveyard.

Tetzin, Gnome Champion // The Golden-Gear Colossus — ruling 4

You may exile tokens you control as part of the materials required. However, because they aren't cards and won't stay in exile, any abilities that refer to what you "used to craft" the back faces won't refer to anything.

Tetzin, Gnome Champion // The Golden-Gear Colossus — ruling 5

If a card that isn't a transforming double-faced card becomes a copy of a card with craft, it'll stay in exile if you activate the craft ability. It won't return to the battlefield.

Tetzin, Gnome Champion // The Golden-Gear Colossus : règles, fonctionnement et interactions (MTG)

Tetzin, Gnome Champion // The Golden-Gear Colossus 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

Whenever Tetzin or another double-faced artifact you control enters, mill three cards. You may put an artifact card from among them into your hand. Craft with six artifacts (, Exile this artifact, Exile the six from among other permanents you control and/or cards from your graveyard: Return this card transformed under its owner's control. Craft only as a sorcery.) Vigilance, trample Whenever The Golden-Gear Colossus enters or attacks, transform up to one other target double-faced artifact you control. Create two 1/1 colorless Gnome artifact creature tokens.

Complete guide

Tetzin, Gnome Champion is a versatile commander that rewards you for playing double-faced artifacts and filling your graveyard. By utilizing the Craft mechanic, he transforms into the massive Golden-Gear Colossus to dominate the battlefield and generate an army of Gnomes. This guide will help you master his unique interaction with transforming permanents and artifact synergies.

Engineering the Engine

While on his front face, Tetzin focuses on resource selection. Whenever he or another double-faced artifact enters your battlefield, you mill three cards. The key advantage here is that you can pick any artifact card from those three to put into your hand, not just double-faced ones. This allows you to dig for utility pieces or specific combo components while building a graveyard full of fodder for his Craft ability.

The Craft Process

To transform Tetzin into The Golden-Gear Colossus, you must pay {4} and exile him along with six other artifacts from your control or your graveyard as a sorcery. Once the ability resolves, he returns to the battlefield transformed. Note that while you can exile tokens to fulfill the 'six artifacts' requirement, they cease to exist in exile and cannot be referenced by 'used to craft' abilities that might appear on other cards.

Colossal Impact

Once transformed, The Golden-Gear Colossus provides immediate value. Whenever he enters or attacks, you create two 1/1 Gnome artifact creature tokens. Additionally, you can transform one other target double-faced artifact you control. This is a powerful way to flip other Craft cards or double-faced permanents without paying their mana costs, provided they are transforming double-faced cards and not modal double-faced cards.

Important Limitations

It is vital to remember that The Golden-Gear Colossus can only transform 'Transforming Double-Faced Cards.' If you target a Modal Double-Faced Card, such as a spell with an artifact on the back, the ability will not cause it to transform. Furthermore, if a creature that is merely a copy of Tetzin tries to use the Craft ability, it will be exiled and fail to return to the battlefield because the physical card is not double-faced.

Interaction examples

Maximizing the Mill

Tetzin, Gnome Champion // The Golden-Gear Colossus

Solemn Simulacrum

When Tetzin, Gnome Champion enters the battlefield, his ability triggers. You mill three cards. If one of those cards is Solemn Simulacrum, you can put it into your hand. This helps you find non-double-faced artifacts to play later, which in turn can be used as fuel for Tetzin's Craft cost once they are in the graveyard or on the field.

Double the Triggers

Tetzin, Gnome Champion // The Golden-Gear Colossus

Roaming Throne

With Roaming Throne on the battlefield naming 'Gnome,' Tetzin's abilities will trigger an additional time. When a double-faced artifact enters, you will mill three cards twice, potentially putting two artifact cards into your hand. When The Golden-Gear Colossus attacks, you will create four Gnome tokens instead of two and can transform two target double-faced artifacts.

Token Production

Tetzin, Gnome Champion // The Golden-Gear Colossus Gnome

Gnome

When The Golden-Gear Colossus enters the battlefield, you create two 1/1 colorless Gnome artifact creature tokens. Because these tokens are artifact creatures, they can be used to block, be sacrificed for value, or even be used as the six required artifacts if you somehow manage to transform Tetzin back to his front face and wish to Craft him again.

Guide written with AI from the official text and rulings. Official English text prevails.

How it works : Tetzin, Gnome Champion // The Golden-Gear Colossus

Original English text — Wizards of the Coast / Scryfall

#1November 10, 2023· Wizards of the Coast
You can target any double-faced artifact you control with The Golden-Gear Colossus's triggered ability, but only transforming double-faced cards and transforming tokens can transform. Choosing an artifact represented by a modal double-faced card (Pestilent Cauldron from Strixhaven, for example) won't cause that permanent to transform.
No other card is named in this ruling.
#2November 10, 2023· Wizards of the Coast
The back faces of some cards with craft refer to cards "used to craft" it. This refers to the cards exiled as part of the cost of the craft ability of the front face. Those cards are considered to be "used to craft" that permanent as long as they remain exiled and the permanent remains on the battlefield, even if the permanent's controller changes or some of its characteristics change (because of a copy effect, for example.)
No other card is named in this ruling.
#3November 10, 2023· Wizards of the Coast
If the materials required include multiple objects, you may exile some of them from among permanents you control and the rest from among cards in your graveyard. You don't have to choose all permanents or all cards from your graveyard.
No other card is named in this ruling.
#4November 10, 2023· Wizards of the Coast
You may exile tokens you control as part of the materials required. However, because they aren't cards and won't stay in exile, any abilities that refer to what you "used to craft" the back faces won't refer to anything.
No other card is named in this ruling.
#5November 10, 2023· Wizards of the Coast
If a card that isn't a transforming double-faced card becomes a copy of a card with craft, it'll stay in exile if you activate the craft ability. It won't return to the battlefield.
No other card is named in this ruling.