If Overzealous Fan's ability is used during combat but the opponent responds with Gust (returning Fan to hand), does the ability still move the attacking unit to the owner's hand?

Ruling: The ability resolves to no effect (whiffs). Since killing Overzealous Fan is a cost-within-instruction required to move the unit, and Fan cannot be killed because it's no longer on the battlefield, the effect cannot be performed.

Sequence:

• Overzealous Fan's ability triggers and is finalized
• Opponent reacts with Gust, returning Fan to hand
• Fan's ability resolves but cannot kill Fan (it's not on battlefield)
• The unit is not moved to owner's hand

Nuances:

• This applies to any effect worded as "do X to do Y" - the first part is a cost paid during resolution that is required for the second part to occur
• The ability has already triggered and finalized by the time you react to it