Ok, so, this is a Rakdos deck. Rakdos likes demons, devils, and imps (but mostly demons) and likes to do the Thanos finger snap on everyone else when he enters the battlefield, so what can we do with a board wipe in the command zone? Quite a bit, it turns out.
When I set out to build this deck, my first goal was to build a cool demon deck. I had had a large demon component in my Sheoldred, Whispering One deck since its inception, but that deck was getting stale and wanted a revamp, so I ended up taking out all the demons from Sheoldred's deck and rehoming most of them in this Rakdos deck. A few didn't make it, such as Kothophed, Soul Hoarder, as his triggered ability was too dangerous with Rakdos and other board wipes so common in the deck.
Once this deck started to take shape, I started to think that I should run other board wipes if I have one in the command zone. However, I wanted to replicate the one-sided nature of Rakdos's effect and so I looked to cards that wouldn't hurt my own creatures, for the most part. This led to me to spells that kill small creatures, spells that kill ground creatures, and one spell that kills nonblack creatures. Traditional full board wipes like Damnation weren't what I wanted here, as I didn't want to lose demons that I'd sunk a fair bit of mana into, and so these alternate wipes can take the slots normally spent on those cards.
With Rakdos's trigger excluding three creature types, I initially set out to not have any creature in the deck that the trigger could kill, but Blood Speaker is too ridiculous of a value engine to pass up in a deck for an expensive tribe like demons. Through whittling down cards into a first build, the deck ended up with only one imp and one devil in it. This wasn't by design but has a pleasing aroma of tokenism to it and fits the deck flavorfully.
A deck focused on an expensive tribe obviously wants a lot of mana ramp and such, so this deck also became a home for the big-mana black card I had also cut from my Sheoldred deck. Being able to hold the board with demons until I can kill with Exsanguinate or Torment of Hailfire is a lot of fun.
While the deck doesn't include a lot of ETB triggers on its creatures (only six in the current build), Conjurer's Closet is worth its slot because of Rakdos alone. Being able to repeatedly halve your opponents' forces is just great. I've even beaten a Liliana, the Last Hope emblem with this combo over the course of about 5 or 6 turns! It's that strong! The other effects you can copy aren't bad either, be it targeted removal, tutoring, or spitting out a bunch of harpy tokens.
That's about all I have to say on this list for now, but as always, I'm happy to answer questions about card choices or consider cards not present in the list. (Note that I've made a few concessions to cool effects and flavorful names over cards that are just better in some cases. If this isn't the deck to run Hellfire in, what is?)
I don't find myself getting too short on life with this deck, so the life gain from Whip and value Exsanguinates is usually more than enough. Disciple of Bolas wouldn't work for the deck as it's not a demon, devil, or imp and doesn't interact with any of those types. I also don't really need sacrifice outlets as I don't want this deck to be a graveyard deck since I have two other graveyard decks already. I'm happy to get a bit of graveyard value but I'm happy to let my creatures die naturally.
Ob of the Black Oath isn't something I want either as only the -2 is something I'd be interested in, and I can get better value than a 5/5 flyer for 3BB.