Gather Courage
Instant
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.)
Target creature gets +2/+2 until end of turn.
Brian Despain
Magic 2015 (M15)
• #175Rulings
Tapping an untapped creature that's attacking or blocking to convoke a spell won't cause that creature to stop attacking or blocking.
(wotc • 2024-01-12)
Tapping a multicolored creature using convoke will pay for {1} or one mana of your choice of any of that creature's colors.
(wotc • 2024-01-12)
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.
(wotc • 2024-01-12)
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.
(wotc • 2024-01-12)
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.
(wotc • 2024-01-12)
Because convoke isn't an alternative cost, it can be used in conjunction with alternative costs.
(wotc • 2024-01-12)
Rulings
Tapping an untapped creature that's attacking or blocking to convoke a spell won't cause that creature to stop attacking or blocking.
(wotc • 2024-01-12)
Tapping a multicolored creature using convoke will pay for {1} or one mana of your choice of any of that creature's colors.
(wotc • 2024-01-12)
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.
(wotc • 2024-01-12)
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.
(wotc • 2024-01-12)
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.
(wotc • 2024-01-12)
Because convoke isn't an alternative cost, it can be used in conjunction with alternative costs.
(wotc • 2024-01-12)