For abilities that deal damage to a target (like Gentlemen's Duel or Teemo Strategist), when must you declare the target - before or after other parts of the ability resolve?

Ruling: You must declare all targets when the ability goes on the chain/stack, before the ability resolves and before any reactions can be played. This applies even when the target is mentioned in the middle or end of the ability text.

Sequence:

• Play the ability card
• Immediately declare all targets (before knowing information like damage amounts)
• The effect goes on the stack
• Priority passes and reactions can be played
• The ability resolves (executing instructions in order)

Nuances:

• If a targeted unit dies before the ability resolves, the ability still resolves but cannot find the target, so nothing happens (the effect is not "negated")
• You have no information about variable effects (like damage amounts from card reveals) before choosing targets
• The active player retains priority after playing the ability and declaring targets, allowing them to play reactions before passing priority