Does Ahri's ability apply to every enemy Unit attacking a battlefield you own, or just one Unit? Does it count as targeting and trigger Deflect?

Ruling: Ahri's ability applies to all enemy Units attacking a battlefield you control. It does not target, so it does not trigger Deflect.

Sequence:

• When an enemy Unit attacks a battlefield you control, Ahri's triggered ability goes on the Chain
• If the same Unit attacks multiple times, the ability triggers each time and the effects stack
• The ability can be responded to with reaction spells since it uses the Chain

Nuances:

• This is a triggered ability (not a passive ability), so it goes on the Chain and can be reacted to
• Triggered abilities are not spells
• If a Unit is moved into combat after combat has started (e.g., with Zenith Blade), Ahri's ability will trigger for that new attacker