DARK Decks?

I was fighting some duelists who use a Pure-DARK Monsters and supports.It don't even have a archetype,just generic DARK monsters with they dark counterparts(Dark Grepher,The Dark Creator,etc)


I ask myself,how I make a good deck with this idea?I made one like that,and uses Dark Horus,The Dark Creator,and Dark Rainbow Dragon.The idea is using Grepher/Armageddon to send Rainbow or Horus to grave,and use CyberDark Fusion to use equip them and have a huge 5000 or 4000 atk beatstick.Using Magical Merchant to mill them and more dark monsters for Dark Creator helps alot too.
They also use Scourge+Phantom Chaos Combo.



Anyway,what you guys know about these decks?