Does Peak Guardian's buff effect work as an aura while it's on the battlefield, or does it only trigger once when played?

Ruling: Peak Guardian only buffs other allied units once when it is played directly to a battlefield. It does not provide an ongoing aura effect.

Sequence:

• Play Peak Guardian to a controlled battlefield
• Peak Guardian buffs all other allied units at that battlefield once
• The buff remains on those units but does not apply to units that arrive later

Nuances:

• Buff is a specific game object, not a generic stat increase like an aura effect
• The card must be played directly to a battlefield for the effect to trigger