Sophic Centaur

{2}{G}{G}, {T}, Discard a card: You gain 2 life for each card in your hand.

Stronghold Biologist

{U}{U}, {T}, Discard a card: Counter target creature spell.

Mountain

Cho-Arrim Alchemist

{1}{W}{W}, {T}, Discard a card: The next time a source of your choice would deal damage to you this turn, prevent that damage. You gain life equal to the damage prevented this way.

Undertaker

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

Mageta the Lion

{2}{W}{W}, {T}, Discard two cards: Destroy all creatures except for Mageta the Lion. Those creatures can't be regenerated.

Llanowar Mentor

{G}, {T}, Discard a card: Create a 1/1 green Elf Druid creature token named Llanowar Elves. It has "{T}: Add {G}."

Avenger en-Dal

{2}{W}, {T}, Discard a card: Exile target attacking creature. Its controller gains life equal to its toughness.

Netter en-Dal

{W}, {T}, Discard a card: Target creature can't attack this turn.

Instigator

{1}{B}{B}, {T}, Discard a card: Creatures target player controls attack this turn if able.

Harvest Mage

{G}, {T}, Discard a card: Until end of turn, if you tap a land for mana, it produces one mana of a color of your choice instead of any other type and amount.

Trickster Mage

{U}, {T}, Discard a card: You may tap or untap target artifact, creature, or land.

Plains

Bone Miser

Whenever you discard a creature card, create a 2/2 black Zombie creature token.
Whenever you discard a land card, add {B}{B}.
Whenever you discard a noncreature, nonland card, draw a card.

Bog Witch

Rushwood Herbalist

{G}, {T}, Discard a card: Regenerate target creature.

Balloon Peddler

{U}, {T}, Discard a card: Target creature gains flying until end of turn.

Echo of Eons

Each player shuffles their hand and graveyard into their library, then draws seven cards.
Flashback {2}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Alexi, Zephyr Mage

{X}{U}, {T}, Discard two cards: Return X target creatures to their owners' hands.

Drake Haven

Whenever you cycle or discard a card, you may pay {1}. If you do, create a 2/2 blue Drake creature token with flying.

Ghost Tactician

{W}, {T}, Discard a card: Creatures you control get +1/+0 until end of turn.

Tolarian Sentinel

Flying
{U}, {T}, Discard a card: Return target permanent you control to its owner's hand.

Jolrael, Empress of Beasts

{2}{G}, {T}, Discard two cards: All lands target player controls become 3/3 creatures until end of turn. They're still lands.

Plague Witch

{B}, {T}, Discard a card: Target creature gets -1/-1 until end of turn.

Bola Warrior

{R}, {T}, Discard a card: Target creature can't block this turn.

Urborg Syphon-Mage

{2}{B}, {T}, Discard a card: Each other player loses 2 life. You gain life equal to the life lost this way.

Flowstone Channeler

{1}{R}, {T}, Discard a card: Target creature gets +1/-1 and gains haste until end of turn.

Blaster Mage

{R}, {T}, Discard a card: Destroy target Wall.

Cackling Witch

{X}{B}, {T}, Discard a card: Target creature gets +X/+0 until end of turn.

Deepwood Drummer

{G}, {T}, Discard a card: Target creature gets +2/+2 until end of turn.

Overtaker

{3}{U}, {T}, Discard a card: Untap target creature and gain control of it until end of turn. That creature gains haste until end of turn.

Hammer Mage

{X}{R}, {T}, Discard a card: Destroy all artifacts with mana value X or less.

Latulla, Keldon Overseer

{X}{R}, {T}, Discard two cards: Latulla, Keldon Overseer deals X damage to any target.

Cloudseeder

Flying
{U}, {T}, Discard a card: Create a 1/1 blue Faerie creature token named Cloud Sprite. It has flying and "Cloud Sprite can block only creatures with flying."

Stampede Driver

{1}{G}, {T}, Discard a card: Creatures you control get +1/+1 and gain trample until end of turn.

Obsessive Search

Draw a card.
Madness {U} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Toymaker

{1}, {T}, Discard a card: Target noncreature artifact becomes an artifact creature with power and toughness each equal to its mana value until end of turn. (It retains its abilities.)

Command Tower

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

Tazri, Stalwart Survivor

Each creature you control has "{T}: Add one mana of any of this creature's colors. Spend this mana only to activate an ability of a creature. Activate only if this creature has another activated ability."
{W}{U}{B}{R}{G}, {T}: Mill five cards. Put all creature cards with activated abilities that aren't mana abilities from among the milled cards into your hand.

Surly Badgersaur

Whenever you discard a creature card, put a +1/+1 counter on Surly Badgersaur.
Whenever you discard a land card, create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")
Whenever you discard a noncreature, nonland card, Surly Badgersaur fights up to one target creature you don't control.

Tonic Peddler

{W}, {T}, Discard a card: Target player gains 3 life.

Divining Witch

{1}{B}, {T}, Discard a card: Choose a card name. Exile the top six cards of your library, then reveal cards from the top of your library until you reveal a card with the chosen name. Put that card into your hand and exile all other cards revealed this way.

Skirk Ridge Exhumer

{B}, {T}, Discard a card: Create a 1/1 black Zombie Goblin creature token named Festering Goblin. It has "When Festering Goblin dies, target creature gets -1/-1 until end of turn."

Sparkspitter

{R}, {T}, Discard a card: Create a 3/1 red Elemental creature token named Spark Elemental. It has trample, haste, and "At the beginning of the end step, sacrifice Spark Elemental."

Icatian Crier

{1}{W}, {T}, Discard a card: Create two 1/1 white Citizen creature tokens.

Damia, Sage of Stone

Deathtouch
Skip your draw step.
At the beginning of your upkeep, if you have fewer than seven cards in hand, draw cards equal to the difference.

Greel, Mind Raker

{X}{B}, {T}, Discard two cards: Target player discards X cards at random.

Kyren Flamewright

{2}{R}, {T}, Discard a card: Create two 1/1 blue and red Elemental creature tokens. Creatures you control get +1/+0 and gain haste until end of turn.

Invasion of Mercadia

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When Invasion of Mercadia enters, you may discard a card. If you do, draw two cards.

Invasion of Mercadia // Kyren Flamewright

Deepwood Elder

{X}{G}{G}, {T}, Discard a card: X target lands become Forests until end of turn.

Ridged Kusite

{1}{B}, {T}, Discard a card: Target creature gets +1/+0 and gains first strike until end of turn.

Swamp

Devout Witness

{1}{W}, {T}, Discard a card: Destroy target artifact or enchantment.

Island

Greenseeker

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

Firefright Mage

{1}{R}, {T}, Discard a card: Target creature can't be blocked this turn except by artifact creatures and/or red creatures.

Sliversmith

{1}, {T}, Discard a card: Create a 1/1 colorless Sliver artifact creature token named Metallic Sliver.

Charm Peddler

{W}, {T}, Discard a card: The next time a source of your choice would deal damage to target creature this turn, prevent that damage.

Arc Mage

{2}{R}, {T}, Discard a card: Arc Mage deals 2 damage divided as you choose among one or two targets.

Notorious Assassin

{2}{B}, {T}, Discard a card: Destroy target nonblack creature. It can't be regenerated.

Dreamscape Artist

{2}{U}, {T}, Discard a card, Sacrifice a land: Search your library for up to two basic land cards, put them onto the battlefield, then shuffle.

Exotic Orchard

{T}: Add one mana of any color that a land an opponent controls could produce.

Dawnstrider

{G}, {T}, Discard a card: Prevent all combat damage that would be dealt this turn.

Jaya Ballard, Task Mage

{R}, {T}, Discard a card: Destroy target blue permanent.
{1}{R}, {T}, Discard a card: Jaya Ballard, Task Mage deals 3 damage to any target. A creature dealt damage this way can't be regenerated this turn.
{5}{R}{R}, {T}, Discard a card: Jaya Ballard deals 6 damage to each creature and each player.

Goldmeadow Lookout

{W}, {T}, Discard a card: Create a 1/1 white Kithkin Soldier creature token named Goldmeadow Harrier. It has "{W}, {T}: Tap target creature."

Stronghold Machinist

{U}{U}, {T}, Discard a card: Counter target noncreature spell.

Waterfront Bouncer

{U}, {T}, Discard a card: Return target creature to its owner's hand.

Silverglade Pathfinder

{1}{G}, {T}, Discard a card: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Diplomatic Escort

{U}, {T}, Discard a card: Counter target spell or ability that targets a creature.