We Ride at Dawn

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.

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.

If you have two commanders and they’re both declared as attackers, We Ride at Dawn’s last ability will trigger twice.

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.

If you control another player’s commander, you won’t create a Mercenary when you attack with that creature. However, if another player controls your commander, you’ll create a Mercenary when it attacks.