Calamity of Cinders — ruling 1

You can tap any untapped creature you control to convoke a spell, even one you haven't controlled continuously since the beginning of your most recent turn.

Calamity of Cinders — ruling 2

If tapping a creature using convoke wouldn't pay for any mana in that spell's cost (because you've already paid for all of the mana in the spell's cost by tapping other creatures or because you've already paid for all of the generic mana in the cost by tapping other creatures and the creature you want to tap doesn't share a color with any of the remaining mana symbols in the spell's cost), you can't use convoke to tap that creature. Effects that increase or reduce the cost of a spell with convoke apply before costs are paid and will increase or decrease the total amount of creatures you can tap.

Calamity of Cinders — ruling 3

When calculating a spell's total cost, include any alternative costs, additional costs, or anything else that increases or reduces the cost to cast the spell. Convoke applies after the total cost is calculated. Convoke doesn't change a spell's mana cost or mana value.

Calamity of Cinders — ruling 4

If a creature you control has a mana ability with {T} in the cost, activating that ability while casting a spell with convoke will result in the creature being tapped before you pay the spell's costs. You won't be able to tap it again for convoke. Similarly, if you sacrifice a creature to activate a mana ability while casting a spell with convoke, that creature won't be on the battlefield when you pay the spell's costs, so you won't be able to tap it for convoke.

Calamity of Cinders — ruling 5

Because convoke isn't an alternative cost, it can be used in conjunction with alternative costs.

Calamity of Cinders — ruling 6

Tapping a multicolored creature using convoke will pay for {1} or one mana of your choice of any of that creature's colors.

Calamity of Cinders : règles, fonctionnement et interactions (MTG)

Calamity of Cinders 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

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for or one mana of that creature's color.) Calamity of Cinders deals 6 damage to each untapped creature.

How it works : Calamity of Cinders

Original English text — Wizards of the Coast / Scryfall

#1July 26, 2024· Wizards of the Coast
You can tap any untapped creature you control to convoke a spell, even one you haven't controlled continuously since the beginning of your most recent turn.
No other card is named in this ruling.
#2July 26, 2024· Wizards of the Coast
If tapping a creature using convoke wouldn't pay for any mana in that spell's cost (because you've already paid for all of the mana in the spell's cost by tapping other creatures or because you've already paid for all of the generic mana in the cost by tapping other creatures and the creature you want to tap doesn't share a color with any of the remaining mana symbols in the spell's cost), you can't use convoke to tap that creature. Effects that increase or reduce the cost of a spell with convoke apply before costs are paid and will increase or decrease the total amount of creatures you can tap.
No other card is named in this ruling.
#3July 26, 2024· Wizards of the Coast
When calculating a spell's total cost, include any alternative costs, additional costs, or anything else that increases or reduces the cost to cast the spell. Convoke applies after the total cost is calculated. Convoke doesn't change a spell's mana cost or mana value.
No other card is named in this ruling.
#4July 26, 2024· Wizards of the Coast
If a creature you control has a mana ability with in the cost, activating that ability while casting a spell with convoke will result in the creature being tapped before you pay the spell's costs. You won't be able to tap it again for convoke. Similarly, if you sacrifice a creature to activate a mana ability while casting a spell with convoke, that creature won't be on the battlefield when you pay the spell's costs, so you won't be able to tap it for convoke.
No other card is named in this ruling.
#5July 26, 2024· Wizards of the Coast
Because convoke isn't an alternative cost, it can be used in conjunction with alternative costs.
No other card is named in this ruling.
#6July 26, 2024· Wizards of the Coast
Tapping a multicolored creature using convoke will pay for or one mana of your choice of any of that creature's colors.
No other card is named in this ruling.