If an artifact on the battlefield has in its mana cost, X is 0 when determining its mana value.
2025-02-07
You choose the target card in your graveyard as Daretti’s second ability is put on the stack, but you don’t choose whether to sacrifice an artifact or which one to sacrifice until the ability resolves.
Daretti's power is equal to the greatest mana value among artifacts you control.
Whenever Daretti enters or attacks, choose target artifact card in your graveyard. You may sacrifice an artifact. If you do, return the chosen card to the battlefield.
in its mana cost, X is 0 when determining its mana value.