Each color in MTG has its characteristic creature type, which is usually a rare or mythic, and demons are the characteristic black creature
In case you've heard the term but don't know the cards, here's a rundown of the original Power Nine: Honorable Mention: Library of Alexandria, arguably Magic's most powerful land, rounds out most people's list of the Power Ten
Regardless of that it is fair to say that tapping your lands to draw cards is more of a tempo cost, particularly in blue, than leaving them open
You just play cards, get rewarded with card draw, then use your new cards to get still more cards until you run out of mana
Sometimes I play this version of the deck regardless of power level just because I like changing it up
This means that effects that can revive the dead also have the potential to slay the undead