Oracle

Instant 

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for 1 or one mana of that creature's color.)
Search your library for a creature card with converted mana cost X or less and put it onto the battlefield. Then shuffle your library.

Tournooi-info

Legal in: Vintage, Legacy, Modern, Commander

Officiele rulings

8/7/2020
If a card in a player’s library has X in its mana cost, X is considered to be 0.

8/7/2020
You can tap an untapped creature you haven’t controlled continuously since the beginning of your most recent turn to convoke a spell.

8/7/2020
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 converted mana cost.

8/7/2020
Tapping a multicolored creature using convoke will pay for 1 or one mana of your choice of any of that creature’s colors.

8/7/2020
When using convoke to cast a spell with X in its mana cost, first choose the value for X. Then you can tap creatures you control to help pay the total cost. For example, if you cast Chord of Calling and choose X to be 3, the total cost is 3GGG. If you tap two green creatures and two white creatures, you’ll have to pay 1G.

8/7/2020
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.

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