Forceful Denial

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
Counter target spell.

Brine Giant

Affinity for enchantments (This spell costs {1} less to cast for each enchantment you control.)

Island

Will-Forged Golem

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)

Gearseeker Serpent

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
{5}{U}: This creature can't be blocked this turn.

Wretched Gryff

Emerge {5}{U} (You may cast this spell by sacrificing a creature and paying the emerge cost reduced by that creature's mana value.)
When you cast this spell, draw a card.
Flying

Spire Golem

Affinity for Islands (This spell costs {1} less to cast for each Island you control.)
Flying

Thunderhead Squadron

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Flying

Sea Gate Colossus

This spell costs {1} less to cast for each creature in your party. (Your party consists of up to one each of Cleric, Rogue, Warrior, and Wizard.)

Depth Charge Colossus

Prototype {4}{U}{U} — 6/6 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.)
This creature doesn't untap during your untap step.
{3}: Untap this creature.

Natural Reclamation

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
Destroy target artifact or enchantment.

Aethersnipe

When this creature enters, return target nonland permanent to its owner's hand.
Evoke {1}{U}{U} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Into Thin Air

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Return target artifact to its owner's hand.

Spellweaver Duo

Assist (Another player can pay up to {6} of this spell's cost.)
When this creature enters, you may return target tapped creature to its owner's hand.

Tangle Golem

Affinity for Forests (This spell costs {1} less to cast for each Forest you control.)

Hamlet Glutton

Bargain (You may sacrifice an artifact, enchantment, or token as you cast this spell.)
This spell costs {2} less to cast if it's bargained.
Trample
When this creature enters, you gain 3 life.

Errant Ephemeron

Flying
Suspend 4—{1}{U} (Rather than cast this card from your hand, you may pay {1}{U} and exile it with four time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost. It has haste.)

Cryptic Serpent

This spell costs {1} less to cast for each instant and sorcery card in your graveyard.

Hooting Mandrills

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Trample

Boulderbranch Golem

Prototype {3}{G} — 3/3 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.)
When this creature enters, you gain life equal to its power.

Drowned Diner

When you unlock this door, draw three cards, then discard a card.
(You may cast either half. That door unlocks on the battlefield. As a sorcery, you may pay the mana cost of a locked door to unlock it.)

Meat Locker

When you unlock this door, tap up to one target creature and put two stun counters on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)
(You may cast either half. That door unlocks on the battlefield. As a sorcery, you may pay the mana cost of a locked door to unlock it.)

Meat Locker // Drowned Diner

Thundering Tanadon

({G/P} can be paid with either {G} or 2 life.)
Trample

Durkwood Baloth

Suspend 5—{G} (Rather than cast this card from your hand, you may pay {G} and exile it with five time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost. It has haste.)

Tolarian Terror

This spell costs {1} less to cast for each instant and sorcery card in your graveyard.
Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)

Annoyed Altisaur

Reach, trample
Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)

Siege Wurm

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Trample

Myr Enforcer

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)

Bastion Inventor

Improvise (Your artifacts can help cast this spell. Each artifact you tap after you're done activating mana abilities pays for {1}.)
Hexproof (This creature can't be the target of spells or abilities your opponents control.)

Sojourner's Companion

Affinity for artifacts
Artifact landcycling {2} ({2}, Discard this card: Search your library for an artifact land card, reveal it, put it into your hand, then shuffle.)

Walker of the Grove

When this creature leaves the battlefield, create a 4/4 green Elemental creature token.
Evoke {4}{G} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Forest

Treasure Cruise

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Draw three cards.

Hand of Emrakul

You may sacrifice four Eldrazi Spawn rather than pay this spell's mana cost.
Annihilator 1 (Whenever this creature attacks, defending player sacrifices a permanent of their choice.)

Imoti, Celebrant of Bounty

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
Spells you cast with mana value 6 or greater have cascade.

Quicksilver Behemoth

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
When this creature attacks or blocks, return it to its owner's hand at end of combat. (Return it only if it's on the battlefield.)

Will of the Naga

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Tap up to two target creatures. Those creatures don't untap during their controller's next untap step.

Charging Binox

Assist (Another player can pay up to {7} of this spell's cost.)
Trample

It of the Horrid Swarm

Emerge {6}{G} (You may cast this spell by sacrificing a creature and paying the emerge cost reduced by that creature's mana value.)
When you cast this spell, create two 1/1 green Insect creature tokens.

Rust Goliath

Prototype {3}{G}{G} — 3/5 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.)
Reach, trample

Maelstrom Colossus

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)

Draconic Lore

This spell costs {2} less to cast if you control a Dragon.
Draw three cards.

Steelfin Whale

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Whenever an artifact you control enters, untap this creature.

Somber Hoverguard

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Flying

Cactarantula

This spell costs {1} less to cast if you control a Desert.
Reach
Whenever this creature becomes the target of a spell or ability an opponent controls, you may draw a card.