Demon of Loathing

Flying, trample
Whenever Demon of Loathing deals combat damage to a player, that player sacrifices a creature.

Kardur's Vicious Return

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — You may sacrifice a creature. When you do, Kardur's Vicious Return deals 3 damage to any target.
II — Each player discards a card.
III — Return target creature card from your graveyard to the battlefield. Put a +1/+1 counter on it. It gains haste until your next turn.

Rakdos Guildgate

Rakdos Guildgate enters the battlefield tapped.
{T}: Add {B} or {R}.

Abhorrent Overlord

Flying
When Abhorrent Overlord enters the battlefield, create a number of 1/1 black Harpy creature tokens with flying equal to your devotion to black. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)
At the beginning of your upkeep, sacrifice a creature.

Discordant Piper

When Discordant Piper dies, create a 0/1 white Goat creature token.

Swamp

Rafter Demon

Spectacle {3}{B}{R} (You may cast this spell for its spectacle cost rather than its mana cost if an opponent lost life this turn.)
When Rafter Demon enters the battlefield, if its spectacle cost was paid, each opponent discards a card.

Unbreakable Bond

Return target creature card from your graveyard to the battlefield with a lifelink counter on it.

Kardur, Doomscourge

When Kardur, Doomscourge enters the battlefield, until your next turn, creatures your opponents control attack each combat if able and attack a player other than you if able.
Whenever an attacking creature dies, each opponent loses 1 life and you gain 1 life.

Ob Nixilis of the Black Oath

+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.

Bloodline Pretender

Changeling (This card is every creature type.)
As Bloodline Pretender enters the battlefield, choose a creature type.
Whenever another creature of the chosen type enters the battlefield under your control, put a +1/+1 counter on Bloodline Pretender.

Thrill of Possibility

As an additional cost to cast this spell, discard a card.
Draw two cards.

Bloodfell Caves

Bloodfell Caves enters the battlefield tapped.
When Bloodfell Caves enters the battlefield, you gain 1 life.
{T}: Add {B} or {R}.

Goremand

As an additional cost to cast this spell, sacrifice a creature.
Flying
Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
When Goremand enters the battlefield, each opponent sacrifices a creature.

Village Rites

As an additional cost to cast this spell, sacrifice a creature.
Draw two cards.

Immersturm Raider

When Immersturm Raider enters the battlefield, you may discard a card. If you do, draw a card.

Mountain

Archfiend of Sorrows

Flying
When Archfiend of Sorrows enters the battlefield, creatures your opponents control get -2/-2 until end of turn.
Unearth {3}{B}{B} ({3}{B}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Fire Prophecy

Fire Prophecy deals 3 damage to target creature. You may put a card from your hand on the bottom of your library. If you do, draw a card.