Playing certain types of temporary events provides a chance to win costume set items. In order to win such items, you need to neutralize enemy cats.
Please keep in mind, the drop chances of costume set items depend on chances. There is no guarantee to complete a costume set within the event duration time.
The chances are the same for all events of this type. Events with seasonal statues are calculated differently.
Be patient and neutralize as many enemy cats as you can during a season to maximize your chances of collecting as many costume items as possible.
Good luck!