Exocrine

Ravenous (This creature enters with X +1/+1 counters on it. If X is 5 or more, draw a card when it enters.)
Bio-plasmic Barrage — When this creature enters, it deals X damage to each player and each other creature.

Judith, Carnage Connoisseur

Whenever you cast an instant or sorcery spell, choose one —
• That spell gains deathtouch and lifelink.
• Create a 2/2 red Imp creature token with "When this token dies, it deals 2 damage to each opponent."

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Tavern Swindler

{T}, Pay 3 life: Flip a coin. If you win the flip, you gain 6 life.

Dualcaster Mage

Flash
When this creature enters, copy target instant or sorcery spell. You may choose new targets for the copy.

Wayfarer's Bauble

{2}, {T}, Sacrifice this artifact: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Priest of Urabrask

When this creature enters, add {R}{R}{R}.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice this artifact: Draw a card.

Carrion Howler

Pay 1 life: This creature gets +2/-1 until end of turn.

Marrow Bats

Flying
Pay 4 life: Regenerate this creature.

Deepwood Ghoul

Imodane, the Pyrohammer

Whenever an instant or sorcery spell you control that targets only a single creature deals damage to that creature, Imodane deals that much damage to each opponent.

Mischievous Poltergeist

Flying
Pay 1 life: Regenerate this creature.

Talisman of Indulgence

{T}: Add {C}.
{T}: Add {B} or {R}. This artifact deals 1 damage to you.

Priest of Gix

When this creature enters, add {B}{B}{B}.

Underworld Connections

Enchant land
Enchanted land has "{T}, Pay 1 life: Draw a card."

Return the Past

During your turn, each instant and sorcery card in your graveyard has flashback. Its flashback cost is equal to its mana cost.

Havoc Festival

Players can't gain life.
At the beginning of each player's upkeep, that player loses half their life, rounded up.

Dark Tutelage

At the beginning of your upkeep, reveal the top card of your library and put that card into your hand. You lose life equal to its mana value.

Street Wraith

Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)
Cycling—Pay 2 life. (Pay 2 life, Discard this card: Draw a card.)

Myr Convert

Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
{T}, Pay 2 life: Add one mana of any color.

Immolating Souleater

{R/P}: This creature gets +1/+0 until end of turn. ({R/P} can be paid with either {R} or 2 life.)

Font of Agonies

Whenever you pay life, put that many blood counters on this enchantment.
{1}{B}, Remove four blood counters from this enchantment: Destroy target creature.

Marshland Bloodcaster

Flying
{1}{B}, {T}: Rather than pay the mana cost of the next spell you cast this turn, you may pay life equal to that spell's mana value.

Magus of the Mirror

{T}, Sacrifice this creature: Exchange life totals with target opponent. Activate only during your upkeep.

Sol Ring

Shadowcloak Vampire

Pay 2 life: This creature gains flying until end of turn. (It can't be blocked except by creatures with flying or reach.)

Soul Channeling

Enchant creature
Pay 2 life: Regenerate enchanted creature.

Demonic Tutor

Search your library for a card, put that card into your hand, then shuffle.

Heartless Hidetsugu

{T}: Heartless Hidetsugu deals damage to each player equal to half that player's life total, rounded down.

Defiler of Instinct

First strike
As an additional cost to cast red permanent spells, you may pay 2 life. Those spells cost {R} less to cast if you paid life this way. This effect reduces only the amount of red mana you pay.
Whenever you cast a red permanent spell, this creature deals 1 damage to any target.

Rakdos Signet

Everflowing Chalice

Multikicker {2} (You may pay an additional {2} any number of times as you cast this spell.)
This artifact enters with a charge counter on it for each time it was kicked.
{T}: Add {C} for each charge counter on this artifact.

Wall of Blood

Defender (This creature can't attack.)
Pay 1 life: This creature gets +1/+1 until end of turn.