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.
6 /
6
{2}{B}{B}{B}
Halo Hunter
Creature - Demon
Intimidate (This creature can't be blocked except by artifact creatures and/or creatures that share a color with it.)
When Halo Hunter enters the battlefield, destroy target Angel.
6 /
3
{3}{B}{B}
Indulgent Tormentor
Creature - Demon
Flying
At the beginning of your upkeep, draw a card unless target opponent sacrifices a creature or pays 3 life.
5 /
3
{4}{B}{B}
Nefarox, Overlord of Grixis
Legendary Creature - Demon
Flying
Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
Whenever Nefarox, Overlord of Grixis attacks alone, defending player sacrifices a creature.
5 /
5
{3}{B}{B}
Ob Nixilis of the Black Oath
Legendary Planeswalker - Nixilis
+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.
L:
3
{4}{B}{B}
Ob Nixilis, Unshackled
Legendary Creature - Demon
Flying, trample
Whenever an opponent searches their library, that player sacrifices a creature and loses 10 life.
Whenever another creature dies, put a +1/+1 counter on Ob Nixilis, Unshackled.
4 /
4
{3}{B}{B}
Ob Nixilis, the Fallen
Legendary Creature - Demon
Landfall -- Whenever a land enters the battlefield under your control, you may have target player lose 3 life. If you do, put three +1/+1 counters on Ob Nixilis, the Fallen.