Harrow

As an additional cost to cast this spell, sacrifice a land.
Search your library for up to two basic land cards, put them onto the battlefield, then shuffle.

Unbound Flourishing

Whenever you cast a permanent spell with a mana cost that contains {X}, double the value of X.
Whenever you cast an instant or sorcery spell or activate an ability, if that spell's mana cost or that ability's activation cost contains {X}, copy that spell or ability. You may choose new targets for the copy.

Hormagaunt Horde

Ravenous (This creature enters with X +1/+1 counters on it. If X is 5 or more, draw a card when it enters.)
Endless Swarm — Whenever a land you control enters, you may pay {2}{G}. If you do, return Hormagaunt Horde from your graveyard to your hand.

Goblin Anarchomancer

Each spell you cast that's red or green costs {1} less to cast.

Fellwar Stone

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

Sulfur Falls

Sulfur Falls enters tapped unless you control an Island or a Mountain.
{T}: Add {U} or {R}.

Termagant Swarm

Ravenous (This creature enters with X +1/+1 counters on it. If X is 5 or more, draw a card when it enters.)
Death Frenzy — When Termagant Swarm dies, create a number of 1/1 green Tyranid creature tokens equal to Termagant Swarm's power.

Chromatic Lantern

Lands you control have "{T}: Add one mana of any color."
{T}: Add one mana of any color.

Kiora's Follower

Izzet Signet

Kodama's Reach

Search your library for up to two basic land cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Hinterland Harbor

Hinterland Harbor enters tapped unless you control a Forest or an Island.
{T}: Add {G} or {U}.

Explore

You may play an additional land this turn.
Draw a card.

Cinder Glade

({T}: Add {R} or {G}.)
Cinder Glade enters tapped unless you control two or more basic lands.

Hydroid Krasis

When you cast this spell, you gain half X life and draw half X cards. Round down each time.
Flying, trample
Hydroid Krasis enters with X +1/+1 counters on it.

Broodlord

Ravenous (This creature enters with X +1/+1 counters on it. If X is 5 or more, draw a card when it enters.)
Brood Telepathy — When Broodlord enters, distribute X +1/+1 counters among any number of other target creatures you control.

Forest

Blasphemous Act

This spell costs {1} less to cast for each creature on the battlefield.
Blasphemous Act deals 13 damage to each creature.

Moss Diamond

Moss Diamond enters tapped.
{T}: Add {G}.

Sporocyst

Ravenous (This creature enters with X +1/+1 counters on it. If X is 5 or more, draw a card when it enters.)
Defender
Spore Chimney — When Sporocyst enters, search your library for up to X basic land cards, put them onto the battlefield tapped, then shuffle.

Magus Lucea Kane

Spiritual Leader — At the beginning of combat on your turn, put a +1/+1 counter on target creature.
Psychic Stimulus — {T}: Add {C}{C}. When you next cast a spell with {X} in its mana cost or activate an ability with {X} in its activation cost this turn, copy that spell or ability. You may choose new targets for the copy. (A copy of a permanent spell becomes a token.)

Evolving Wilds

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

Fire Diamond

Fire Diamond enters tapped.
{T}: Add {R}.

Mawloc

Ravenous (This creature enters with X +1/+1 counters on it. If X is 5 or more, draw a card when it enters.)
Terror from the Deep — When Mawloc enters, it fights up to one target creature an opponent controls. If that creature would die this turn, exile it instead.

Talisman of Creativity

{T}: Add {C}.
{T}: Add {U} or {R}. Talisman of Creativity deals 1 damage to you.

Chain Reaction

Chain Reaction deals X damage to each creature, where X is the number of creatures on the battlefield.

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 Exocrine enters, it deals X damage to each player and each other creature.

Urban Evolution

Draw three cards. You may play an additional land this turn.

Tyrant Guard

Ravenous (This creature enters with X +1/+1 counters on it. If X is 5 or more, draw a card when it enters.)
Shieldwall — Sacrifice Tyrant Guard: Creatures you control with counters on them gain hexproof and indestructible until end of turn.

Karplusan Forest

{T}: Add {C}.
{T}: Add {R} or {G}. Karplusan Forest deals 1 damage to you.

Gruul Signet

Decanter of Endless Water

You have no maximum hand size.
{T}: Add one mana of any color.

Wild Growth

Enchant land
Whenever enchanted land is tapped for mana, its controller adds an additional {G}.

Terramorphic Expanse

{T}, Sacrifice Terramorphic Expanse: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Elementalist's Palette

Whenever you cast a spell with {X} in its mana cost, put two charge counters on Elementalist's Palette.
{T}: Add one mana of any color.
{T}: Add {C} for each charge counter on Elementalist's Palette. Spend this mana only on costs that contain {X}.

Animist's Awakening

Reveal the top X cards of your library. Put all land cards from among them onto the battlefield tapped and the rest on the bottom of your library in a random order.
Spell mastery — If there are two or more instant and/or sorcery cards in your graveyard, untap those lands.

Utopia Sprawl

Enchant Forest
As Utopia Sprawl enters, choose a color.
Whenever enchanted Forest is tapped for mana, its controller adds an additional one mana of the chosen color.

Inspiring Call

Draw a card for each creature you control with a +1/+1 counter on it. Those creatures gain indestructible until end of turn. (Damage and effects that say "destroy" don't destroy them.)

Command Tower

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

Shivan Devastator

Flying, haste
Shivan Devastator enters with X +1/+1 counters on it.

Stonecoil Serpent

Reach, trample, protection from multicolored
Stonecoil Serpent enters with X +1/+1 counters on it.

Frontier Bivouac

Frontier Bivouac enters tapped.
{T}: Add {G}, {U}, or {R}.

Thought Vessel

You have no maximum hand size.
{T}: Add {C}.

Arcane Signet

Rockfall Vale

Rockfall Vale enters tapped unless you control two or more other lands.
{T}: Add {R} or {G}.

Tervigon

Ravenous (This creature enters with X +1/+1 counters on it. If X is 5 or more, draw a card when it enters.)
Trample
Spawn Termagants — Whenever Tervigon deals combat damage to a player, create that many 1/1 green Tyranid creature tokens.

Thran Dynamo

Sol Ring

Liquimetal Torque

{T}: Add {C}.
{T}: Target nonland permanent becomes an artifact in addition to its other types until end of turn.

Talisman of Impulse

{T}: Add {C}.
{T}: Add {R} or {G}. Talisman of Impulse deals 1 damage to you.

Rampant Growth

Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Yavimaya Coast

{T}: Add {C}.
{T}: Add {G} or {U}. Yavimaya Coast deals 1 damage to you.

Gilded Lotus

Sky Diamond

Altered Ego

This spell can't be countered.
You may have Altered Ego enter as a copy of any creature on the battlefield, except it enters with X additional +1/+1 counters on it.

Sakura-Tribe Elder

Sacrifice Sakura-Tribe Elder: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Reckless Endeavor

Roll two d12 and choose one result. Reckless Endeavor deals damage equal to that result to each creature. Then create a number of Treasure tokens equal to the other result.

Mountain

Island

Simic Signet

Primordial Hydra

Primordial Hydra enters with X +1/+1 counters on it.
At the beginning of your upkeep, double the number of +1/+1 counters on Primordial Hydra.
Primordial Hydra has trample as long as it has ten or more +1/+1 counters on it.

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice Mind Stone: Draw a card.

Nature's Lore

Search your library for a Forest card, put that card onto the battlefield, then shuffle.

Worn Powerstone

Worn Powerstone enters tapped.
{T}: Add {C}{C}.

Growth Spiral

Draw a card. You may put a land card from your hand onto the battlefield.

Voracious Hydra

Trample
Voracious Hydra enters with X +1/+1 counters on it.
When Voracious Hydra enters, choose one —
• Double the number of +1/+1 counters on Voracious Hydra.
• Voracious Hydra fights target creature you don't control.

Hedron Archive

{T}: Add {C}{C}.
{2}, {T}, Sacrifice this artifact: Draw two cards.

Open the Way

X can't be greater than the number of players in the game.
Reveal cards from the top of your library until you reveal X land cards. Put those land cards onto the battlefield tapped and the rest on the bottom of your library in a random order.

Cultivate

Shivan Reef

{T}: Add {C}.
{T}: Add {U} or {R}. Shivan Reef deals 1 damage to you.

Heroic Intervention

Permanents you control gain hexproof and indestructible until end of turn.

Commander's Sphere

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

Skyshroud Claim

Search your library for up to two Forest cards, put them onto the battlefield, then shuffle.