Callous Oppressor

You may choose not to untap Callous Oppressor during your untap step.
As Callous Oppressor enters, an opponent chooses a creature type.
{T}: Gain control of target creature that isn't of the chosen type for as long as Callous Oppressor remains tapped.

Llawan, Cephalid Empress

When Llawan, Cephalid Empress enters, return all blue creatures your opponents control to their owners' hands.
Your opponents can't cast blue creature spells.

Eluge, the Shoreless Sea

Eluge's power and toughness are each equal to the number of Islands you control.
Whenever Eluge enters or attacks, put a flood counter on target land. It's an Island in addition to its other types for as long as it has a flood counter on it.
The first instant or sorcery spell you cast each turn costs {U} (or {1}) less to cast for each land you control with a flood counter on it.

Minamo, School at Water's Edge

{T}: Add {U}.
{U}, {T}: Untap target legendary permanent.

Theft of Dreams

Draw a card for each tapped creature target opponent controls.

Cephalid Broker

{T}: Target player draws two cards, then discards two cards.

Rapid Hybridization

Destroy target creature. It can't be regenerated. That creature's controller creates a 3/3 green Frog Lizard creature token.

Giant Octopus

Verity Circle

Whenever a creature an opponent controls becomes tapped, if it isn't being declared as an attacker, you may draw a card.
{4}{U}: Tap target creature without flying.

Urza's Incubator

As Urza's Incubator enters, choose a creature type.
Creature spells of the chosen type cost {2} less to cast.

Sol Ring

Patchwork Banner

As Patchwork Banner enters, choose a creature type.
Creatures you control of the chosen type get +1/+1.
{T}: Add one mana of any color.

Amoeboid Changeling

Changeling (This card is every creature type.)
{T}: Target creature gains all creature types until end of turn.
{T}: Target creature loses all creature types until end of turn.

Counterspell

Borrowing 100,000 Arrows

Birthing Boughs

{4}, {T}: Create a 2/2 colorless Shapeshifter creature token with changeling. (It has every creature type.)

Defiler of Dreams

Flying
As an additional cost to cast blue permanent spells, you may pay 2 life. Those spells cost {U} less to cast if you paid life this way. This effect reduces only the amount of blue mana you pay.
Whenever you cast a blue permanent spell, draw a card.

Vanquisher's Banner

As Vanquisher's Banner enters, choose a creature type.
Creatures you control of the chosen type get +1/+1.
Whenever you cast a creature spell of the chosen type, draw a card.

Aetherize

Return all attacking creatures to their owner's hand.

Obelisk of Urd

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.)
As Obelisk of Urd enters, choose a creature type.
Creatures you control of the chosen type get +2/+2.

Omen Hawker

{T}: Add {C}{U}. Spend this mana only to activate abilities.

Mothdust Changeling

Changeling (This card is every creature type.)
Tap an untapped creature you control: Mothdust Changeling gains flying until end of turn.

Arcane Signet

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

Tidal Terror

Whenever Tidal Terror attacks, you may tap two other untapped creatures you control. If you do, Tidal Terror can't be blocked this turn.
Islandcycling {2} ({2}, Discard this card: Search your library for an Island card, reveal it, put it into your hand, then shuffle.)

Halimar Depths

Halimar Depths enters tapped.
When Halimar Depths enters, look at the top three cards of your library, then put them back in any order.
{T}: Add {U}.

Cephalid Pathmage

Cephalid Pathmage can't be blocked.
{T}, Sacrifice Cephalid Pathmage: Target creature can't be blocked this turn.

Cephalid Looter

{T}: Target player draws a card, then discards a card.

Cephalid Vandal

At the beginning of your upkeep, put a shred counter on Cephalid Vandal. Then mill a card for each shred counter on Cephalid Vandal.

Sapphire Medallion

Blue spells you cast cost {1} less to cast.

Cephalid Constable

Whenever Cephalid Constable deals combat damage to a player, return up to that many target permanents that player controls to their owner's hand.

Whelming Wave

Return all creatures to their owners' hands except for Krakens, Leviathans, Octopuses, and Serpents.

Shapesharer

Changeling (This card is every creature type.)
{2}{U}: Target Shapeshifter becomes a copy of target creature until your next turn.

Backstreet Bruiser

Defender
As long as there are two or more counters among creatures you control, Backstreet Bruiser can attack as though it didn't have defender.

Dramatic Reversal

Untap all nonland permanents you control.

Serpent of Yawning Depths

Krakens, Leviathans, Octopuses, and Serpents you control can't be blocked except by Krakens, Leviathans, Octopuses, and Serpents.

Reliquary Tower

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

Universal Automaton

Changeling (This card is every creature type.)

Cephalid Inkshrouder

Discard a card: Cephalid Inkshrouder 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.)

Metallic Mimic

As Metallic Mimic enters, choose a creature type.
Metallic Mimic is the chosen type in addition to its other types.
Each other creature you control of the chosen type enters with an additional +1/+1 counter on it.

Shield Broker

When Shield Broker enters, put a shield counter on target noncommander creature you don't control. You gain control of that creature for as long as it has a shield counter on it. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)

Faces of the Past

Whenever a creature dies, tap all untapped creatures that share a creature type with it or untap all tapped creatures that share a creature type with it.

Wonder

Flying
As long as Wonder is in your graveyard and you control an Island, creatures you control have flying.

Cephalid Scout

Flying
{2}{U}, Sacrifice a land: Draw a card.

Island

Caged Sun

As Caged Sun enters, choose a color.
Creatures you control of the chosen color get +1/+1.
Whenever a land's ability causes you to add one or more mana of the chosen color, add one additional mana of that color.

Cyclonic Rift

Return target nonland permanent you don't control to its owner's hand.
Overload {6}{U} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Acquisition Octopus

Whenever Acquisition Octopus or equipped creature deals combat damage to a player, draw a card.
Reconfigure {2} ({2}: Attach to target creature you control; or unattach from a creature. Reconfigure only as a sorcery. While attached, this isn't a creature.)

Laboratory Maniac

If you would draw a card while your library has no cards in it, you win the game instead.

Icewrought Sentry

Vigilance
Whenever Icewrought Sentry attacks, you may pay {1}{U}. When you do, tap target creature an opponent controls.
Whenever you tap an untapped creature an opponent controls, Icewrought Sentry gets +2/+1 until end of turn.

Hylda's Crown of Winter

{1}, {T}: Tap target creature. This ability costs {1} less to activate during your turn.
{3}, Sacrifice Hylda's Crown of Winter: Draw a card for each tapped creature your opponents control.

Mesmerizing Benthid

When Mesmerizing Benthid enters, create two 0/2 blue Illusion creature tokens with "Whenever this creature blocks a creature, that creature doesn't untap during its controller's next untap step."
Mesmerizing Benthid has hexproof as long as you control an Illusion.

Sea-Dasher Octopus

Mutate {1}{U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Flash
Whenever this creature deals combat damage to a player, draw a card.

Unctus, Grand Metatect

Other blue creatures you control have "Whenever this creature becomes tapped, draw a card, then discard a card."
Other artifact creatures you control get +1/+1.
{U/P}: Until end of turn, target creature you control becomes a blue artifact in addition to its other colors and types. Activate only as a sorcery. ({U/P} can be paid with either {U} or 2 life.)

Cephalid Sage

Threshold — As long as seven or more cards are in your graveyard, Cephalid Sage has "When Cephalid Sage enters, draw three cards, then discard two cards."

Mutavault

{T}: Add {C}.
{1}: Mutavault becomes a 2/2 creature with all creature types until end of turn. It's still a land.

Adaptive Automaton

As this creature enters, choose a creature type.
This creature is the chosen type in addition to its other types.
Other creatures you control of the chosen type get +1/+1.

Cephalid Facetaker

Cephalid Facetaker can't be blocked.
At the beginning of combat on your turn, you may have Cephalid Facetaker become a copy of another target creature until end of turn, except it's 1/4 and has "This creature can't be blocked."

Archetype of Imagination

Creatures you control have flying.
Creatures your opponents control lose flying and can't have or gain flying.

Bubble Smuggler

Disguise {5}{U} (You may cast this card face down for {3} as a 2/2 creature with ward {2}. Turn it face up any time for its disguise cost.)
As Bubble Smuggler is turned face up, put four +1/+1 counters on it.

Path of Ancestry

Path of Ancestry enters tapped.
{T}: Add one mana of any color in your commander's color identity. When that mana is spent to cast a creature spell that shares a creature type with your commander, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Cavern of Souls

As Cavern of Souls enters, choose a creature type.
{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a creature spell of the chosen type, and that spell can't be countered.

Bloodline Pretender

Changeling (This card is every creature type.)
As Bloodline Pretender enters, choose a creature type.
Whenever another creature you control of the chosen type enters, put a +1/+1 counter on Bloodline Pretender.

Godhunter Octopus

Godhunter Octopus can't attack unless defending player controls an enchantment or an enchanted permanent.

High Tide

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

Cephalid Illusionist

Whenever Cephalid Illusionist becomes the target of a spell or ability, mill three cards.
{2}{U}, {T}: Prevent all combat damage that would be dealt to and dealt by target creature you control this turn.

Decanter of Endless Water

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

Psychic Pickpocket

When Psychic Pickpocket enters, it connives. When it connives this way, return up to one target nonland permanent to its owner's hand. (To have a creature connive, draw a card, then discard a card. If you discarded a nonland card, put a +1/+1 counter on that creature.)

Deluge

Octoprophet

When Octoprophet enters, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Reflections of Littjara

As Reflections of Littjara enters, choose a creature type.
Whenever you cast a spell of the chosen type, copy that spell. (A copy of a permanent spell becomes a token.)

Spawning Kraken

Whenever a Kraken, Leviathan, Octopus, or Serpent you control deals combat damage to a player, create a 9/9 blue Kraken creature token.

Aboshan, Cephalid Emperor

Tap an untapped Octopus you control: Tap target permanent.
{U}{U}{U}: Tap all creatures without flying.