Flow of Ideas

Kasmina's Transmutation

Enchant creature
Enchanted creature loses all abilities and has base power and toughness 1/1.

Supplant Form

Return target creature to its owner's hand. You create a token that's a copy of that creature.

Reweave

Target permanent's controller sacrifices it. If the player does, they reveal cards from the top of their library until they reveal a permanent card that shares a card type with the sacrificed permanent, put that card onto the battlefield, then shuffle.
Splice onto Arcane {2}{U}{U} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Jalira, Master Polymorphist

{2}{U}, {T}, Sacrifice another creature: Reveal cards from the top of your library until you reveal a nonlegendary creature card. Put that card onto the battlefield and the rest on the bottom of your library in a random order.

Aetherspouts

For each attacking creature, its owner puts it on their choice of the top or bottom of their library.

Negate

Flayer Husk

Living weapon (When this Equipment enters, create a 0/0 black Phyrexian Germ creature token, then attach this to it.)
Equipped creature gets +1/+1.
Equip {2}

Summoner's Bane

Counter target creature spell. Create a 2/2 blue Illusion creature token.

Bonehoard

Living weapon (When this Equipment enters, create a 0/0 black Phyrexian Germ creature token, then attach this to it.)
Equipped creature gets +X/+X, where X is the number of creature cards in all graveyards.
Equip {2}

Saheeli's Artistry

Choose one or both —
• Create a token that's a copy of target artifact.
• Create a token that's a copy of target creature, except it's an artifact in addition to its other types.

Artisan of Kozilek

When you cast this spell, you may return target creature card from your graveyard to the battlefield.
Annihilator 2 (Whenever this creature attacks, defending player sacrifices two permanents of their choice.)

Lazotep Plating

Amass Zombies 1. (Put a +1/+1 counter on an Army you control. It's also a Zombie. If you don't control an Army, create a 0/0 black Zombie Army creature token first.)
You and permanents you control gain hexproof until end of turn. (You and they can't be the targets of spells or abilities your opponents control.)

Stormtide Leviathan

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
All lands are Islands in addition to their other types.
Creatures without flying or islandwalk can't attack.

High Tide

Until end of turn, whenever a player taps an Island for mana, that player adds an additional {U}.

Palladium Myr

Thopter Spy Network

At the beginning of your upkeep, if you control an artifact, create a 1/1 colorless Thopter artifact creature token with flying.
Whenever one or more artifact creatures you control deal combat damage to a player, draw a card.

Rise from the Tides

Create a tapped 2/2 black Zombie creature token for each instant and sorcery card in your graveyard.

Engulf the Shore

Return to their owners' hands all creatures with toughness less than or equal to the number of Islands you control.

Ichthyomorphosis

Enchant creature
Enchanted creature loses all abilities and is a blue Fish with base power and toughness 0/1.

Geist Snatch

Counter target creature spell. Create a 1/1 blue Spirit creature token with flying.

Talrand's Invocation

Create two 2/2 blue Drake creature tokens with flying.

Inkwell Leviathan

Trample
Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Shroud (This creature can't be the target of spells or abilities.)

Reef Worm

When Reef Worm dies, create a 3/3 blue Fish creature token with "When this creature dies, create a 6/6 blue Whale creature token with 'When this creature dies, create a 9/9 blue Kraken creature token.'"

Mind Stone

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

Divination

Drownyard Behemoth

Flash (You may cast this spell any time you could cast an instant.)
Emerge {7}{U} (You may cast this spell by sacrificing a creature and paying the emerge cost reduced by that creature's mana value.)
Drownyard Behemoth has hexproof as long as it entered this turn.

Tidal Force

At the beginning of each upkeep, you may tap or untap target permanent.

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.)

Concentrate

Polymorphous Rush

Strive — This spell costs {1}{U} more to cast for each target beyond the first.
Choose a creature on the battlefield. Any number of target creatures you control each become a copy of that creature until end of turn.

Crush Dissent

Counter target spell unless its controller pays {2}.
Amass Zombies 2. (Put two +1/+1 counters on an Army you control. It's also a Zombie. If you don't control an Army, create a 0/0 black Zombie Army creature token first.)

Island

Rise of Eagles

Create two 2/2 blue Bird enchantment creature tokens with flying. Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Ojutai's Summons

Create a 2/2 blue Djinn Monk creature token with flying.
Rebound (If you cast this spell from your hand, exile it as it resolves. At the beginning of your next upkeep, you may cast this card from exile without paying its mana cost.)

Goliath Sphinx

Displacement Wave

Return all nonland permanents with mana value X or less to their owners' hands.

Mana Geode

When Mana Geode enters, scry 1.
{T}: Add one mana of any color.

Temple of the False God

{T}: Add {C}{C}. Activate only if you control five or more lands.

Counterspell

Mortarpod

Living weapon (When this Equipment enters, create a 0/0 black Phyrexian Germ creature token, then attach this to it.)
Equipped creature gets +0/+1 and has "Sacrifice this creature: This creature deals 1 damage to any target."
Equip {2}

Followed Footsteps

Enchant creature
At the beginning of your upkeep, create a token that's a copy of enchanted creature.

Stolen Identity

Create a token that's a copy of target artifact or creature.
Cipher (Then you may exile this spell card encoded on a creature you control. Whenever that creature deals combat damage to a player, its controller may cast a copy of the encoded card without paying its mana cost.)

Skywise Teachings

Whenever you cast a noncreature spell, you may pay {1}{U}. If you do, create a 2/2 blue Djinn Monk creature token with flying.

Metallurgic Summonings

Whenever you cast an instant or sorcery spell, create an X/X colorless Construct artifact creature token, where X is that spell's mana value.
{3}{U}{U}, Exile Metallurgic Summonings: Return all instant and sorcery cards from your graveyard to your hand. Activate only if you control six or more artifacts.

Sickleslicer

Living weapon (When this Equipment enters, create a 0/0 black Phyrexian Germ creature token, then attach this to it.)
Equipped creature gets +2/+2.
Equip {4}

Sol Ring

Eldrazi Devastator

Skinwing

Living weapon (When this Equipment enters, create a 0/0 black Phyrexian Germ creature token, then attach this to it.)
Equipped creature gets +2/+2 and has flying.
Equip {6}

Darksteel Ingot

Indestructible (Effects that say "destroy" don't destroy this artifact.)
{T}: Add one mana of any color.

Thran Dynamo

Blue Sun's Zenith

Target player draws X cards. Shuffle Blue Sun's Zenith into its owner's library.

Aviation Pioneer

When Aviation Pioneer enters, create a 1/1 colorless Thopter artifact creature token with flying.

Guile

Guile can't be blocked except by three or more creatures.
If a spell or ability you control would counter a spell, instead exile that spell and you may play that card without paying its mana cost.
When Guile is put into a graveyard from anywhere, shuffle it into its owner's library.

Polymorph

Destroy target creature. It can't be regenerated. Its controller reveals cards from the top of their library until they reveal a creature card. The player puts that card onto the battlefield, then shuffles all other cards revealed this way into their library.

Cancel

Mass Polymorph

Exile all creatures you control, then reveal cards from the top of your library until you reveal that many creature cards. Put all creature cards revealed this way onto the battlefield, then shuffle the rest of the revealed cards into your library.

Fountain of Ichor

{T}: Add one mana of any color.
{3}: Fountain of Ichor becomes a 3/3 Dinosaur artifact creature until end of turn.

Curse of the Swine

Exile X target creatures. For each creature exiled this way, its controller creates a 2/2 green Boar creature token.

Efficient Construction

Whenever you cast an artifact spell, create a 1/1 colorless Thopter artifact creature token with flying.

Synthetic Destiny

Exile all creatures you control. At the beginning of the next end step, reveal cards from the top of your library until you reveal that many creature cards, put all creature cards revealed this way onto the battlefield, then shuffle the rest of the revealed cards into your library.

Frogify

Enchant creature
Enchanted creature loses all abilities and is a blue Frog creature with base power and toughness 1/1. (It loses all other card types and creature types.)

Ulamog's Crusher

Annihilator 2 (Whenever this creature attacks, defending player sacrifices two permanents of their choice.)
Ulamog's Crusher attacks each combat if able.

Proteus Staff

{2}{U}, {T}: Put target creature on the bottom of its owner's library. That creature's controller reveals cards from the top of their library until they reveal a creature card. The player puts that card onto the battlefield and the rest on the bottom of their library in any order. Activate only as a sorcery.

Nevinyrral's Disk

Nevinyrral's Disk enters tapped.
{1}, {T}: Destroy all artifacts, creatures, and enchantments.

Springjack Pasture

{T}: Add {C}.
{4}, {T}: Create a 0/1 white Goat creature token.
{T}, Sacrifice X Goats: Add X mana of any one color. You gain X life.

Slinn Voda, the Rising Deep

Kicker {1}{U} (You may pay an additional {1}{U} as you cast this spell.)
When Slinn Voda, the Rising Deep enters, if it was kicked, return all creatures to their owners' hands except for Merfolk, Krakens, Leviathans, Octopuses, and Serpents.