Chord of Calling

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

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

When using convoke to cast a spell with {X} in its mana cost, first choose the value for X. That choice, plus any cost increases or decreases, will determine the spell's total cost. Then you can tap creatures you control to help pay that cost. For example, if you cast Chord of Calling (a spell with convoke and mana cost {X}{G}{G}{G}) and choose X to be 3, the total cost is {3}{G}{G}{G}. If you tap two green creatures and two red creatures, you'll have to pay {1}{G}.

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

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.

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.