Can an opponent buff their units in response to Teemo Strategist's ability before the damage is dealt?

Ruling: Yes, the opponent can use reactions to buff their units after Teemo's ability goes on the chain but before the damage is dealt.

Sequence:

• Teemo's ability goes onto the chain
• Opponent has a chance to use reactions
• Cards are revealed and damage is dealt

Nuances:

• The opponent must react before knowing how much damage Teemo will do (before cards are revealed)