Everything in the Sworn To Darkness Commander deck: all 100 cards with current prices, what the deck is worth against the sealed price, the 15 new cards, and whether it is worth buying.
+2: Each opponent loses 1 life. You gain life equal to the life lost this way. −2: Create a 5/5 black Demon creature token with flying. You lose 2 life. −8: You get an emblem with "{1}{B}, Sacrifice a creature: You gain X life and draw X cards, where X is the sacrificed creature's power." Ob Nixilis of the Black Oath can be your commander.
Maybe I have a soft spot for a good villain, but Sworn to Darkness effectively captures the iconic black Magic deck. It kills stuff, makes risky trades for the Promise of Power, and trades in its (honestly kind of valuable) creatures for things like Xathrid Demon.
I kept Sworn to Darkness together unmodified in its original box for years so I could use it to teach new players how to play Commander. It’s an excellent deck for beginners because it covers almost all the main concepts and interactions that’ll happen over the course of a game and most of the cards aren’t incredibly complex to play around.
Ob Nixilis is also an over-the-top grimdark character, and I love him for it. As part of the promotional material for Commander 2014 WotC published a short story about his origins, in which he kills his entire home plane to ignite his spark. No other human in Magic has done a genocide on this level, except maybe Urza if you count that whole “destroying Serra’s plane to power his spaceboat” thing.
Sworn to Darkness is a deck built around death, dying, and being dead. In classic black form it showcases removal spells and sacrifice outlets to kill just about everything it can. The deck’s face commander, Ob Nixilis of the Black Oath, takes its place as evil overlord of the deck supported by Ghoulcaller Gisa and Drana, Kalastria Bloodchief.
Ob Nixilis himself is all the gas you need to get that value engine going. It’ll trade you life for demon tokens and then drain your opponents’ life, rinse and repeat!