Demons on a budget. Uses creature recursion and sacrifice-for-mana effects to quickly play an abundance of demons. Can win through reducing opponents' lives to zero or with Liliana's Contract.
If you're wondering, "Why isn't <this card> in the deck?" then check the price. If it's over a dollar, that's probably why. While I do make some exceptions, I generally try to keep my budget decks with most of the cards costing less than a dollar.
First, a few terms:
HD = Hungry Demons a.k.a. demons that may require you to sacrifice or destroy a creature: Reaper from the Abyss, Shadowborn Demon.
MA = Mana Accelerators: Bubbling Muck, Dark Ritual, Liliana's Shade, Liturgy of Blood, Priest of Gix, Witch Engine.
Search = Cards that let you search your library for other cards: Diabolic Tutor, Final Parting, Mausoleum Secrets, Night Dealings, Razaketh's Rite.
SRC = Self-Recursive Creature: Bloodsoaked Champion, Brood of Cockroaches, Reassembling Skeleton, Sanitarium Skeleton.
SMA = Sacrificial Mana Accelerators: Blood Pet, Blood Vassal, Basal Sliver, Basal Thrull, Bog Witch (not technically a sacrifice, but you have to give up a card), Overeager Apprentice, Ruthless Knave, Sacrifice, Soldevi Adnate.
Fodder = Low-casting cost creatures used to block early game until you can get demons and used for sacrifices in the later parts of the game: Deathgreeter, Typhoid Rats, Ruthless Ripper, SRCs, SMAs, etc.
[*] In the early game, play as much Fodder as you can. Use a combination of SRCs and SMAs to get the mana needed to cast as many demons as possible. Play four demons and Liliana's Contract as soon as possible. Try to kill your opponent the old-fashioned way while you're trying to get demons and Liliana's Contract.
[*] HDs can be fed with SRCs.
[*] Use Search cards to get Haunted Crossroads and/or Palace Siege, any demons you need and Liliana's Contract.
[*] Creatures who are going to die anyway (excessive combat damage, removal effects, etc) should be sacrificed to the Ruthless Knave's ability before the effect killing the creature resolves.
[*] Sacrificing Havoc Demon to the Soldevi Adnate can help wipe most creatures off the board and give you mana to cast another Demon.
[*] Once Haunted Crossroads and/or Palace Siege hits the battlefield, every creature becomes an SRC.
[*] Liliana's Contract and some demons cause a loss of life. This can be countered with Deathgreeter and Krav, the Unredeemed's ability.
[*] Feed Krav with SRCs which will also trigger the Deathgreeeter's ability.
[*] Put Witch Engine's ability on the stack then sacrifice it to Soldevi Adnate. That gives you 10 black mana to use and your opponent doesn't get the Witch Engine.
[*] To get the best use out of Priest of Gix, sacrifice it to Soldevi Adnate right after you play it. You get the three mana when it comes into play, replacing what you spent to cast it, then three more mana for sacrificing it to the Soldevi Adnate.
[*] Blood Speaker and Haunted Crossroads can be used to get you a demon every turn.
[*] Eater of Hope, Kindly Stranger/Demon-Possessed Witch, and Haunted Crossroads can be used for recursive creature removal.