Covenant of Blood — ruling 1

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.

Covenant of Blood — ruling 2

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.

Covenant of Blood — ruling 3

Tapping an untapped creature that's attacking or blocking to convoke a spell won't cause that creature to stop attacking or blocking.

Covenant of Blood — ruling 4

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

Covenant of Blood — ruling 5

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.

Covenant of Blood — ruling 6

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

Covenant of Blood — ruling 7

If the target permanent or player is an illegal target when Covenant of Blood tries to resolve, it won't resolve and none of its effects will happen. You won't gain any life. (Any creatures you tapped to cast Covenant of Blood remain tapped.)

Covenant of Blood : règles, fonctionnement et interactions (MTG)

Covenant of Blood 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.) Covenant of Blood deals 4 damage to any target and you gain 4 life.

How it works : Covenant of Blood

Original English text — Wizards of the Coast / Scryfall

#1January 12, 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.
#2January 12, 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.
#3January 12, 2024· Wizards of the Coast
Tapping an untapped creature that's attacking or blocking to convoke a spell won't cause that creature to stop attacking or blocking.
No other card is named in this ruling.
#4January 12, 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.
#5January 12, 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.
#6January 12, 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.
#7July 18, 2014· Wizards of the Coast
If the target permanent or player is an illegal target when Covenant of Blood tries to resolve, it won't resolve and none of its effects will happen. You won't gain any life. (Any creatures you tapped to cast Covenant of Blood remain tapped.)
No other card is named in this ruling.