Can an opponent use Gust to remove the target unit when playing Cruel Patron, and if so, does Cruel Patron still resolve?

Ruling: Cruel Patron cannot be responded to with Gust. Killing a unit is an additional cost paid when playing Cruel Patron, so the unit is already dead before any player can react. Additionally, as a permanent without triggered abilities, Cruel Patron enters and leaves the chain immediately without giving priority to either player.

Sequence:

• You begin playing Cruel Patron
• You choose the location for Cruel Patron
• You pay costs (including killing a unit as an additional cost)
• Legality is checked after costs are paid
• Cruel Patron enters play immediately without priority being given
• No opportunity exists to react with Gust

Nuances:

• If there is no legal unit to kill when finalizing the play (after costs are paid), Cruel Patron fails to be played and returns to where it was before without entering the chain
• If playing Cruel Patron to a battlefield with only one unit and you kill that unit as the cost, the play becomes illegal and is undone since the battlefield must have an empty location