Unexpected Fangs

Put a +1/+1 counter and a lifelink counter on target creature.

Pollywog Symbiote

Each creature spell you cast costs {1} less to cast if it has mutate.
Whenever you cast a creature spell, if it has mutate, draw a card, then discard a card.

Artful Takedown

Choose one or both —
• Tap target creature.
• Target creature gets -2/-4 until end of turn.

Archipelagore

Mutate {5}{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.)
Whenever this creature mutates, tap up to X target creatures, where X is the number of times this creature has mutated. Those creatures don't untap during their controller's next untap step.

Cancel

Chittering Harvester

Mutate {4}{B} (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.)
Whenever this creature mutates, each opponent sacrifices a creature of their choice.

Dismal Backwater

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {U} or {B}.

Evolving Wilds

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

Insatiable Hemophage

Mutate {2}{B} (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.)
Deathtouch
Whenever this creature mutates, each opponent loses X life and you gain X life, where X is the number of times this creature has mutated.

Duress

Target opponent reveals their hand. You choose a noncreature, nonland card from it. That player discards that card.

Dead Weight

Enchant creature
Enchanted creature gets -2/-2.

Essence Scatter

Keep Safe

Counter target spell that targets a permanent you control.
Draw a card.

Island

Swamp

Zagoth Mamba

Whenever this creature mutates, target creature an opponent controls gets -2/-2 until end of turn.

Dimir Guildgate

This land enters tapped.
{T}: Add {U} or {B}.

Bladebrand

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

Serrated Scorpion

When Serrated Scorpion dies, it deals 2 damage to each opponent and you gain 2 life.

Thought Collapse

Counter target spell. Its controller mills three cards.

Thieving Otter

Whenever Thieving Otter deals damage to an opponent, draw a card.

Cavern Whisperer

Mutate {3}{B} (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.)
Menace (This creature can't be blocked except by two or more creatures.)
Whenever this creature mutates, each opponent discards a card.

House Guildmage

{1}{U}, {T}: Target creature doesn't untap during its controller's next untap step.
{2}{B}, {T}: Surveil 2. (Look at the top two cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)

Pouncing Shoreshark

Mutate {3}{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 mutates, you may return target creature an opponent controls to its owner's hand.