Gobhobbler Rats

Hellbent — As long as you have no cards in hand, Gobhobbler Rats gets +1/+0 and has "{B}: Regenerate Gobhobbler Rats." (The next time it would be destroyed, instead tap it, remove it from combat, and heal all damage on it.)

Fiery Temper

Fiery Temper deals 3 damage to any target.
Madness {R} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Avatar of Discord

({B/R} can be paid with either {B} or {R}.)
Flying
When Avatar of Discord enters the battlefield, sacrifice it unless you discard two cards.

Pain Magnification

Whenever an opponent is dealt 3 or more damage by a single source, that player discards a card.

Infernal Tutor

Reveal a card from your hand. Search your library for a card with the same name as that card, reveal it, put it into your hand, then shuffle.
Hellbent — If you have no cards in hand, instead search your library for a card, put it into your hand, then shuffle.

Demonfire

Demonfire deals X damage to any target. If a creature dealt damage this way would die this turn, exile it instead.
Hellbent — If you have no cards in hand, this spell can't be countered and the damage can't be prevented.

Twinstrike

Twinstrike deals 2 damage to each of two target creatures.
Hellbent — Destroy those creatures instead if you have no cards in hand.

Rakdos Augermage

First strike
{T}: Reveal your hand and discard a card of target opponent's choice. Then that player reveals their hand and discards a card of your choice. Activate only as a sorcery.

Anthem of Rakdos

Whenever a creature you control attacks, it gets +2/+0 until end of turn and Anthem of Rakdos deals 1 damage to you.
Hellbent — As long as you have no cards in hand, if a source you control would deal damage to a permanent or player, it deals double that damage to that permanent or player instead.

Skullmead Cauldron

{T}: You gain 1 life.
{T}, Discard a card: You gain 3 life.

Swamp

Dark Withering

Destroy target nonblack creature.
Madness {B} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Ignorant Bliss

Exile all cards from your hand face down. At the beginning of the next end step, return those cards to your hand, then draw a card.

Hellhole Rats

Haste
When Hellhole Rats enters the battlefield, target player discards a card. Hellhole Rats deals damage to that player equal to that card's mana value.

Necrogoyf

Necrogoyf's power is equal to the number of creature cards in all graveyards.
At the beginning of each player's upkeep, that player discards a card.
Madness {1}{B}{B} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Rix Maadi, Dungeon Palace

{T}: Add {C}.
{1}{B}{R}, {T}: Each player discards a card. Activate only as a sorcery.

Jagged Poppet

Whenever Jagged Poppet is dealt damage, discard that many cards.
Hellbent — Whenever Jagged Poppet deals combat damage to a player, if you have no cards in hand, that player discards cards equal to the damage.

Wrecking Ball

Terminal Agony

Destroy target creature.
Madness {B}{R} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Drekavac

When Drekavac enters the battlefield, sacrifice it unless you discard a noncreature card.

Rain of Gore

If a spell or ability would cause its controller to gain life, that player loses that much life instead.

Rakdos Carnarium

Rakdos Carnarium enters the battlefield tapped.
When Rakdos Carnarium enters the battlefield, return a land you control to its owner's hand.
{T}: Add {B}{R}.

Bottled Cloister

At the beginning of each opponent's upkeep, exile all cards from your hand face down.
At the beginning of your upkeep, return all cards you own exiled with Bottled Cloister to your hand, then draw a card.

Mountain

Cackling Flames

Cackling Flames deals 3 damage to any target.
Hellbent — Cackling Flames deals 5 damage instead if you have no cards in hand.

Abyssal Nocturnus

Whenever an opponent discards a card, Abyssal Nocturnus gets +2/+2 and gains fear until end of turn. (It can't be blocked except by artifact creatures and/or black creatures.)

Rakdos Pit Dragon

{R}{R}: Rakdos Pit Dragon gains flying until end of turn.
{R}: Rakdos Pit Dragon gets +1/+0 until end of turn.
Hellbent — Rakdos Pit Dragon has double strike as long as you have no cards in hand.

Delirium Skeins

Rakdos the Defiler

Flying, trample
Whenever Rakdos the Defiler attacks, sacrifice half the non-Demon permanents you control, rounded up.
Whenever Rakdos deals combat damage to a player, that player sacrifices half the non-Demon permanents they control, rounded up.

Lyzolda, the Blood Witch

{2}, Sacrifice a creature: Lyzolda, the Blood Witch deals 2 damage to any target if the sacrificed creature was red. Draw a card if the sacrificed creature was black.