the masters of chaos are made up of villains from across the multiverse that have been defeated by their respective heroes from their respective dimensions before as they are the new most dangerous arch-enemies and dark counterparts of the mane 8 (twilight sparkle and applejack and fluttershy and pinkie pie and rainbow dash and starlight glimmer and sunset shimmer) and their purple dragon friend spike the dragon and the cutie mark crusaders (my little pony friendship is magic) which takes place after the defeat of the legion of doom (my little pony friendship is magic) but before the events of the next generation of my little pony and after the events of kingdom hearts remind (which basically is a remastered version of kingdom hearts 3) which the main members are 

malice (real name xelyk) who is the mastermind of this team and is a former member of the true organization 13

and

striker from helluva boss is the gunslinger and malice's second in command 

and

negaduck (jim starling) from disney xd's ducktales 2017 is the weapons maker and deadly master of combat

and

airachnid from transformers prime is the dark mistress of the insecticons 

and

bowser koopa from the super mario bros 2023 animated movie series is the king of koopas

and 

doctor ivo robotnik from paramount's sonic cinematic universe is the mad genius 

and

tomura shigaraki and himiko toga and dabi from my hero academia anime series are the next generation of villains

and

darth maul from star wars is the force user and lightsaber wielder