Emperor of Darkness is a Monarch structure deck.
Monarchs playstyle is like the old yu gi oh style. It's all about tribute summons and using your spell cards and trap cards to support your monsters.
This is the cheapest deck that you can get that can play decently out of the box.
I would suggest that if you're planning to get the deck you should buy 3 so it's more complete but you could play with just one if you're playing casually with friends.
Some of the cards got nerfed really really hard so if you're planning to play on tourneys then I would suggest on getting another deck such as the dinosmasher's fury as it hasn't been nerfed yet or the pendulum domination both of which are available here for purchase.