How does the buff in Rally the Troops work?

According to the RiftJudge FAQ (#600) and the card's mechanics, here is how the buff in Rally the Troops works:

• Continuous Effect: Rally the Troops does not just buff the next unit played; it creates a global, turn-long condition. Each time a friendly unit is played (or a token is created, per FAQ #418) for the remainder of that turn, a delayed trigger is placed on the chain to apply a buff to that unit.
• Buff Mechanics: A "buff" in Riftbound refers specifically to placing a Buff counter on a unit (Rule 426.1). Per Rule 702.3, a unit can only have one buff at a time. If you play a unit that already has a buff, it will not receive another one (Rule 426.1.b.1).
• Bonus Might: Each individual buff provides +1 Might to the unit (Rule 703).
• Tokens: This effect applies to unit tokens created by other cards as well, unless the card text specifically excludes them (RiftJudge FAQ #418).

In summary, Rally the Troops functions as a persistent effect for the turn that grants a buff counter to every friendly unit you play or create, provided those units are eligible to receive a buff (i.e., they don't already have one).