When playing a spell that buffs a unit, does the opponent get to react before or after you select the target unit?

Ruling: You must select the target unit before your opponent can react. Defining targets is part of the process of putting the effect on the chain, so targets must be chosen before any player gets priority to respond.

Sequence:

• Choose the target unit as you put the spell on the chain
• The spell is finalized (placed on the chain)
• Priority passes and opponent can now react
• If no reactions, the spell resolves and the buff is applied

Nuances:

• This applies to all spells that require choosing objects, not just buff spells (e.g., Hidden Blade also requires target selection before reactions)
• The active player (who cast the spell) gets first priority to play reactions after their own spell is finalized
• Some cards like Falling Star are exceptions where targeting happens during resolution rather than when putting on the chain
• Cards with costs paid on resolution (like Miss Fortune signature) only require choosing the battlefield target initially, with the payment amount decided on resolution