When defending with Teemo Strategist, when can the opponent react to the ability - before or after revealing cards and targeting a unit?

Ruling: The opponent can react before you reveal cards.

Sequence:

• Teemo Strategist's ability triggers
• Opponent has opportunity to react
• Cards are revealed and unit is targeted
• Ability resolves

Nuances:

• If a Nocturne is revealed, it will be played immediately as it's added to the chain as a pending item, and once Teemo is done resolving, pending items are finalized in the order they were added (regardless of who has priority in combat)