The objective of this deck is simple: overwhelm your opponents one by one with big angry Demons.
Tsabo isn't crucial to the workings of the deck, but she's in the right colors. Cast her if you have enough mana floating and nothing else to spend it on. Her abilities are useful to get rid of annoying enemy Commanders.
The manabase is aimed towards black, but there are BR lands in there to cast Tsabo or hardcast Sire of Insanity, Rakdos or Master of Cruelties.
There are lots of Shadowborn Apostles (SAs) in the deck so that you are likely to draw them fast - statistics says you have a 97.7% chance of drawing at least one in your opening hand.
The Demons are your powerhouses. Demon of Death's Gate is a 9/9 beater. Archdemon of Unx can turn your 1/1 SAs into 2/2 Zombies in a pinch, while Hollowborn Barghest combos well with Sire of Insanity. Lord of the Void mills out your opponents while strengthening your board position, and Master of Cruelties is perfect for setting up an opponent for another player to take out in their turn. Pestilence Demon takes care of any weak creatures, but beware, as it will kill any SAs you have.
Rakdos the Defiler might be my least favorite of the Demons because of his first ability, but his second is excellent - it's basically a situational Annihilator. Bring him out late-game to make the most of him while he will hurt you less. Rune-Scarred Demon tutors for any card in your deck (I recommend Thrumming Stone), and Sire of Insanity prevents any players from planning too far ahead.
Your artifacts are important. Elbrus becomes a 13/13 who gets +13/+13 when another player loses - beware, as this often makes you a target. Elixir of Immortality gets you back SAs and Demons, and stalls mill decks. Lightning Greaves and Swiftfoot Boots help your Demons survive and attack quickly, while Skullclamp gets rid of pesky 1-toughness creatures, swaps SAs for cards, or makes your Demons a bit more powerful. Teferi's Puzzle Box is more disruption, and Thrumming Stone gets your SAs out faster and in greater numbers by thinning cards that aren't SAs from the top of your deck.
Most of the spells are mana accelerants or draw power. This means you can quickly and efficiently get out your SAs and use them to bring out your Demons. Hero's Downfall and Dreadbore are excellent removal.
