Chasm Skulker

Whenever you draw a card, put a +1/+1 counter on Chasm Skulker.
When Chasm Skulker dies, create X 1/1 blue Squid creature tokens with islandwalk, where X is the number of +1/+1 counters on Chasm Skulker. (They can't be blocked as long as defending player controls an Island.)

Mirari

Whenever you cast an instant or sorcery spell, you may pay {3}. If you do, copy that spell. You may choose new targets for the copy.

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.)

Daring Apprentice

{T}, Sacrifice Daring Apprentice: Counter target spell.

Daze

You may return an Island you control to its owner's hand rather than pay this spell's mana cost.
Counter target spell unless its controller pays {1}.

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."

Cephalid Broker

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

Stronghold Machinist

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

Surrakar Spellblade

Whenever you cast an instant or sorcery spell, you may put a charge counter on Surrakar Spellblade.
Whenever Surrakar Spellblade deals combat damage to a player, you may draw X cards, where X is the number of charge counters on it.

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.

Eyes of the Watcher

Whenever you cast an instant or sorcery spell, you may pay {1}. If you do, 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.)

Remove Soul

Relic Amulet

Whenever you cast an instant, sorcery, or Wizard spell, put a charge counter on Relic Amulet.
{2}, {T}, Remove all charge counters from Relic Amulet: It deals that much damage to target creature.

Shapesharer

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

Dissolve

Counter target spell. Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Rewind

Counter target spell. Untap up to four lands.

Cloak of Feathers

Target creature gains flying until end of turn.
Draw a card.

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.

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.

Churning Eddy

Return target creature and target land to their owners' hands.

Wind Sail

One or two target creatures gain flying until end of turn.

Swarm Intelligence

Whenever you cast an instant or sorcery spell, you may copy that spell. You may choose new targets for the copy.

Tidal Surge

Tap up to three target creatures without flying.

Littjara Kinseekers

Changeling (This card is every creature type.)
When Littjara Kinseekers enters, if you control three or more creatures that share a creature type, put a +1/+1 counter on Littjara Kinseekers, then scry 1.

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.

Mistwalker

Changeling (This card is every creature type.)
Flying
{1}{U}: Mistwalker gets +1/-1 until end of turn.

Cephalid Looter

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

Reflective Golem

Whenever you cast an instant or sorcery spell that targets only Reflective Golem, you may pay {2}. If you do, copy that spell. You may choose new targets for the copy.

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.)

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.

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.)

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.

Undo

Return two target creatures to their owners' hands.

Forbid

Buyback—Discard two cards. (You may discard two cards in addition to any other costs as you cast this spell. If you do, put this card into your hand as it resolves.)
Counter target spell.

Force Spike

Counter target spell unless its controller pays {1}.

Wings of Velis Vel

Changeling (This card is every creature type.)
Until end of turn, target creature has base power and toughness 4/4, gains all creature types, and gains flying.

Coastal Piracy

Whenever a creature you control deals combat damage to an opponent, you may draw a card.

Aboshan, Cephalid Emperor

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

Disrupt

Counter target instant or sorcery spell unless its controller pays {1}.
Draw a card.

Mothdust Changeling

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

Sphinx-Bone Wand

Whenever you cast an instant or sorcery spell, you may put a charge counter on Sphinx-Bone Wand. If you do, Sphinx-Bone Wand deals damage equal to the number of charge counters on it to any target.

Spell Blast

Counter target spell with mana value X. (For example, if that spell's mana cost is {3}{U}{U}, X is 5.)

Invisibility

Enchant creature
Enchanted creature can't be blocked except by Walls.

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.

Mana Leak

Counter target spell unless its controller pays {3}.

Counterspell

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.

Stronghold Biologist

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

Ego Erasure

Changeling (This card is every creature type.)
Creatures target player controls get -2/-0 and lose all creature types until end of turn.

Awesome Presence

Enchant creature
Enchanted creature can't be blocked unless defending player pays {3} for each creature they control that's blocking it.

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.

Flash Counter

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.

Island

Octavia, Living Thesis

This spell costs {8} less to cast if you have eight or more instant and/or sorcery cards in your graveyard.
Ward {8}
Magecraft — Whenever you cast or copy an instant or sorcery spell, target creature has base power and toughness 8/8 until end of turn.

Turtleshell Changeling

Changeling (This card is every creature type.)
{1}{U}: Switch Turtleshell Changeling's power and toughness until end of turn.

Arm with Aether

Until end of turn, creatures you control gain "Whenever this creature deals damage to an opponent, you may return target creature that player controls to its owner's hand."

Dissipate

Counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Cephalid Pathmage

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

Niblis of Frost

Flying
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you cast an instant or sorcery spell, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

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.

Windrider Wizard

Flying
Whenever you cast an instant, sorcery, or Wizard spell, you may draw a card. If you do, discard a card.

Rethink

Counter target spell unless its controller pays {X}, where X is its mana value.

Touch of Invisibility

Target creature can't be blocked this turn.
Draw a card.

Orvar, the All-Form

Changeling
Whenever you cast an instant or sorcery spell, if it targets one or more other permanents you control, create a token that's a copy of one of those permanents.
When a spell or ability an opponent controls causes you to discard this card, create a token that's a copy of target permanent.

Disruptive Student

{T}: Counter target spell unless its controller pays {1}.

Power Sink

Counter target spell unless its controller pays {X}. If that player doesn't, they tap all lands with mana abilities they control and lose all unspent mana.

Grazilaxx, Illithid Scholar

Whenever a creature you control becomes blocked, you may return it to its owner's hand.
Whenever one or more creatures you control deal combat damage to a player, draw a card.