you can reduce (or at least try , ofc , since the last combination has low odds in general. Luckly this event has 2x increased chance if i remember corectly ) the cost of a cc-ed unit with the basic un-cced one , but you have to keep in mind that some units change skill after cc (like aria , so you won't get a skill up if you combine the cc-ed aria with an basic aria. If you also want the skill up , u can try to cc the basic coppy at level 30 and use it as fodder for main aria after ) , so keep that in mind when combining units to raise the skill.