Tetzin, Gnome Champion
Legendary Artifact Creature — Gnome
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.)
The Golden-Gear Colossus
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Legendary Artifact Creature — GnomeVigilance, 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.
The sum is greater than the parts.
Kekai Kotaki
Rulings
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.
(wotc • 2023-11-10)
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.)
(wotc • 2023-11-10)
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.
(wotc • 2023-11-10)
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.
(wotc • 2023-11-10)
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.
(wotc • 2023-11-10)
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Rulings
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.
(wotc • 2023-11-10)
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.)
(wotc • 2023-11-10)
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.
(wotc • 2023-11-10)
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.
(wotc • 2023-11-10)
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.
(wotc • 2023-11-10)