A couple of cards that can be used are Dark Cavalry, Chaos Ritual Monster, and the Advanced Ritual. While the Structure deck might not have the best cards for the Dark Magician archetype, it does have various powerful cards you can use to build the ultimate Magician deck. The archetype was targeted by multiple bans due to how strong it is and is a great starting point for this archetype. Masters of Chaos decks use various Magicians to create the strongest Magician your opponents have seen.