Unconditional

Cephalid Inkshrouder

Discard a card: This creature gains shroud until end of turn and can't be blocked this turn. (A creature with shroud can't be the target of spells or abilities.)

Call the Bloodline

{1}, Discard a card: Create a 1/1 black Vampire Knight creature token with lifelink. Activate only once each turn.

Noose Constrictor

Reach
Discard a card: This creature gets +1/+1 until end of turn.

Solphim, Mayhem Dominus

If a source you control would deal noncombat damage to an opponent or a permanent an opponent controls, it deals double that damage to that player or permanent instead.
{1}{R/P}{R/P}, Discard two cards: Put an indestructible counter on Solphim. ({R/P} can be paid with either {R} or 2 life.)

Cabal Initiate

Discard a card: This creature gains lifelink until end of turn.
Threshold — This creature gets +1/+2 as long as seven or more cards are in your graveyard.

Survival of the Fittest

{G}, Discard a creature card: Search your library for a creature card, reveal that card, put it into your hand, then shuffle.

Dream Trawler

Flying, lifelink
Whenever you draw a card, this creature gets +1/+0 until end of turn.
Whenever this creature attacks, draw a card.
Discard a card: This creature gains hexproof until end of turn. Tap it.

Trained Pronghorn

Discard a card: Prevent all damage that would be dealt to this creature this turn.

Peace of Mind

Unconditional/Land

Ayula's Influence

Discard a land card: Create a 2/2 green Bear creature token.

Guardian of New Benalia

Enlist (As this creature attacks, you may tap a nonattacking creature you control without summoning sickness. When you do, add its power to this creature's until end of turn.)
Whenever this creature enlists a creature, scry 2.
Discard a card: This creature gains indestructible until end of turn. Tap it.

Psychic Frog

Whenever this creature deals combat damage to a player or planeswalker, draw a card.
Discard a card: Put a +1/+1 counter on this creature.
Exile three cards from your graveyard: This creature gains flying until end of turn.

Necromancer's Stockpile

{1}{B}, Discard a creature card: Draw a card. If the discarded card was a Zombie card, create a tapped 2/2 black Zombie creature token.

Tomb Robber

Menace
{1}, Discard a card: This creature explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

Unconditional/Creature

Lotleth Troll

Trample
Discard a creature card: Put a +1/+1 counter on this creature.
{B}: Regenerate this creature.

Geralf's Masterpiece

Flying
This creature gets -1/-1 for each card in your hand.
{3}{U}, Discard three cards: Return this card from your graveyard to the battlefield tapped.

Tireless Tribe

Discard a card: This creature gets +0/+4 until end of turn.

Unconditional/Artifact

Fleshgrafter

Discard an artifact card: This creature gets +2/+2 until end of turn.

Hypochondria

{W}, Discard a card: Prevent the next 3 damage that would be dealt to any target this turn.
{W}, Sacrifice this enchantment: Prevent the next 3 damage that would be dealt to any target this turn.

Putrid Imp

Discard a card: This creature gains flying until end of turn.
Threshold — As long as seven or more cards are in your graveyard, this creature gets +1/+1 and can't block.

Scuttletide

{1}, Discard a card: Create a 0/3 blue Crab creature token.
Delirium — Crabs you control get +1/+1 as long as there are four or more card types among cards in your graveyard.

Phantatog

Sacrifice an enchantment: This creature gets +1/+1 until end of turn.
Discard a card: This creature gets +1/+1 until end of turn.

Chromium, the Mutable

Flash
This spell can't be countered.
Flying
Discard a card: Until end of turn, Chromium becomes a Human with base power and toughness 1/1, loses all abilities, and gains hexproof. It can't be blocked this turn.

Seismic Assault

Discard a land card: This enchantment deals 2 damage to any target.

Harnfel, Horn of Bounty

Discard a card: Exile the top two cards of your library. You may play those cards this turn.

Birgi, God of Storytelling

Whenever you cast a spell, add {R}. Until end of turn, you don't lose this mana as steps and phases end.
Creatures you control can boast twice during each of your turns rather than once.

Birgi, God of Storytelling // Harnfel, Horn of Bounty

Attunement

Return this enchantment to its owner's hand: Draw three cards, then discard four cards.

Zombie Infestation

Discard two cards: Create a 2/2 black Zombie creature token.

Anurid Brushhopper

Discard two cards: Exile this creature. Return it to the battlefield under its owner's control at the beginning of the next end step.

Chivalric Alliance

Whenever you attack with two or more creatures, draw a card.
{2}, Discard a card: Create a 2/2 white and blue Knight creature token with vigilance.

Ghostly Pilferer

Whenever this creature becomes untapped, you may pay {2}. If you do, draw a card.
Whenever an opponent casts a spell from anywhere other than their hand, draw a card.
Discard a card: This creature can't be blocked this turn.

Earsplitting Rats

When this creature enters, each player discards a card.
Discard a card: Regenerate this creature.

Merciless Javelineer

{2}, Discard a card: Put a -1/-1 counter on target creature. That creature can't block this turn.

Volrath's Dungeon

Pay 5 life: Destroy this enchantment. Any player may activate this ability but only during their turn.
Discard a card: Target player puts a card from their hand on top of their library. Activate only as a sorcery.

Compulsion

{1}{U}, Discard a card: Draw a card.
{1}{U}, Sacrifice this enchantment: Draw a card.

Fleeting Spirit

{W}, Exile three cards from your graveyard: This creature gains first strike until end of turn.
Discard a card: Exile this creature. Return it to the battlefield under its owner's control at the beginning of the next end step.

Escape Artist

This creature can't be blocked.
{U}, Discard a card: Return this creature to its owner's hand.

Wild Mongrel

Discard a card: This creature gets +1/+1 and becomes the color of your choice until end of turn.

Yawgmoth, Thran Physician

Protection from Humans
Pay 1 life, Sacrifice another creature: Put a -1/-1 counter on up to one target creature and draw a card.
{B}{B}, Discard a card: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Oblivion Crown

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature
Enchanted creature has "Discard a card: This creature gets +1/+1 until end of turn."

Trade Routes

{1}: Return target land you control to its owner's hand.
{1}, Discard a land card: Draw a card.

Mindless Automaton

This creature enters with two +1/+1 counters on it.
{1}, Discard a card: Put a +1/+1 counter on this creature.
Remove two +1/+1 counters from this creature: Draw a card.

Flowstone Sculpture

{2}, Discard a card: Put a +1/+1 counter on this creature or this creature gains flying, first strike, or trample. (This effect lasts indefinitely.)

Chainer, Nightmare Adept

Discard a card: You may cast a creature spell from your graveyard this turn. Activate only once each turn.
Whenever a nontoken creature you control enters, if you didn't cast it from your hand, it gains haste until your next turn.

Pack Rat

Pack Rat's power and toughness are each equal to the number of Rats you control.
{2}{B}, Discard a card: Create a token that's a copy of this creature.

Insidious Mist

Hexproof, indestructible
This creature can't block and can't be blocked.
Whenever this creature attacks and isn't blocked, you may pay {2}{B}. If you do, transform it.

Elusive Tormentor

{1}, Discard a card: Transform this creature.

Elusive Tormentor // Insidious Mist

Saproling Cluster

{1}, Discard a card: Create a 1/1 green Saproling creature token. Any player may activate this ability.

Glint-Eye Nephilim

Whenever this creature deals combat damage to a player, draw that many cards.
{1}, Discard a card: This creature gets +1/+1 until end of turn.

Soul of Windgrace

Whenever Soul of Windgrace enters or attacks, you may put a land card from a graveyard onto the battlefield tapped under your control.
{G}, Discard a land card: You gain 3 life.
{1}{R}, Discard a land card: Draw a card.
{2}{B}, Discard a land card: Soul of Windgrace gains indestructible until end of turn. Tap it.

Mortiphobia

{1}{B}, Discard a card: Exile target card from a graveyard.
{1}{B}, Sacrifice this enchantment: Exile target card from a graveyard.

Prognostic Sphinx

Flying
Discard a card: This creature gains hexproof until end of turn. Tap it.
Whenever this creature attacks, scry 3.

Nihilistic Glee

{2}{B}, Discard a card: Target opponent loses 1 life and you gain 1 life.
Hellbent — {1}, Pay 2 life: Draw a card. Activate only if you have no cards in hand.

Nature's Blessing

{G}{W}, Discard a card: Put a +1/+1 counter on target creature or that creature gains banding, first strike, or trample. (This effect lasts indefinitely. Any creatures with banding, and up to one without, can attack in a band. Bands are blocked as a group. If any creatures with banding a player controls are blocking or being blocked by a creature, that player divides that creature's combat damage, not its controller, among any of the creatures it's being blocked by or is blocking.)

Tortured Existence

{B}, Discard a creature card: Return target creature card from your graveyard to your hand.

Psychatog

Discard a card: This creature gets +1/+1 until end of turn.
Exile two cards from your graveyard: This creature gets +1/+1 until end of turn.

Phantasmagorian

When you cast this spell, any player may discard three cards. If a player does, counter Phantasmagorian.
Discard three cards: Return this card from your graveyard to your hand.

Mind Over Matter

Discard a card: You may tap or untap target artifact, creature, or land.

Skirge Familiar

Ormos, Archive Keeper

Flying
If you would draw a card while your library has no cards in it, instead put five +1/+1 counters on Ormos.
{1}{U}{U}, Discard three cards with different names: Draw five cards.

Nezahal, Primal Tide

This spell can't be countered.
You have no maximum hand size.
Whenever an opponent casts a noncreature spell, draw a card.
Discard three cards: Exile Nezahal. Return it to the battlefield tapped under its owner's control at the beginning of the next end step.