Which dc villains typically appear in major crossover events?

The sources supplied contain information about the DC Universe as a shared media franchise and its continuity strategy, but they do not list individual villains or describe their participation in crossover events. Because no verified evidence addresses specific DC villains in crossovers, the answer must reflect that absence of data rather than speculate. If you need details about particular villains, consult dedicated comic or cinematic resources that discuss crossover storylines.