When does the opponent select their target for Cull the Weak - at cast or resolution?

Ruling: Targets for Cull the Weak are selected when the spell resolves, not when it is cast. When Cull the Weak is played, no units are selected yet and priority passes to the opponent to respond.

Sequence:

• Player casts Cull the Weak
• Priority passes to opponent (no targets selected yet)
• Opponent may respond with effects like Hidden Blade
• Cull the Weak resolves
• Both players select their units

Nuances:

• A player cannot select their unit as the Cull target and then use Hidden Blade on it, because Hidden Blade must be played before Cull resolves (which is before unit selection happens)