Huskburster Swarm

This spell costs {1} less to cast for each creature card you own in exile and in your graveyard.
Menace, deathtouch

Hermetic Study

Enchant creature
Enchanted creature has "{T}: This creature deals 1 damage to any target."

Ovinize

Until end of turn, target creature loses all abilities and has base power and toughness 0/1.

Hyalopterous Lemure

{0}: Hyalopterous Lemure gets -1/-0 and gains flying until end of turn.

Frantic Search

Draw two cards, then discard two cards. Untap up to three lands.

Nightscape Familiar

Blue spells and red spells you cast cost {1} less to cast.
{1}{B}: Regenerate Nightscape Familiar.

Horseshoe Crab

Murky Sewer

Murky Sewer enters tapped unless a player has 13 or less life.
{T}: Add {U} or {B}.

Sporogenic Infection

Enchant creature
When Sporogenic Infection enters, target player sacrifices a creature of their choice other than enchanted creature.
When enchanted creature is dealt damage, destroy it.

Malice

Destroy target nonblack creature. It can't be regenerated.

Spite

Spite // Malice

Counterspell

Terramorphic Expanse

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

Psychic Frog

Whenever Psychic Frog deals combat damage to a player or planeswalker, draw a card.
Discard a card: Put a +1/+1 counter on Psychic Frog.
Exile three cards from your graveyard: Psychic Frog gains flying until end of turn.

Thundertrap Trainer

Offspring {4} (You may pay an additional {4} as you cast this spell. If you do, when this creature enters, create a 1/1 token copy of it.)
When this creature enters, look at the top four cards of your library. You may reveal a noncreature, nonland card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Inundated Archive

Inundated Archive enters tapped.
{T}: Add {U} or {B}.

Waterlogged Teachings

Search your library for an instant card or a card with flash, reveal it, put it into your hand, then shuffle.

Waterlogged Teachings // Inundated Archive

Arcanis the Omnipotent

{T}: Draw three cards.
{2}{U}{U}: Return Arcanis to its owner's hand.

Sneaky Snacker

Flying
When you draw your third card in a turn, return Sneaky Snacker from your graveyard to the battlefield tapped.

Ophiomancer

At the beginning of each upkeep, if you control no Snakes, create a 1/1 black Snake creature token with deathtouch.

Fell Mire

As Fell Mire enters, you may pay 3 life. If you don't, it enters tapped.
{T}: Add {B}.

Fell the Profane

Fell the Profane // Fell Mire

Copycrook

You may have Copycrook enter as a copy of any creature on the battlefield, except it has "Whenever this creature attacks, it connives." (Draw a card, then discard a card. If you discarded a nonland card, put a +1/+1 counter on this creature.)

Leaden Fists

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature
Enchanted creature gets +3/+3 and doesn't untap during its controller's untap step.

Fell

Thieving Magpie

Flying (This creature can't be blocked except by creatures with flying or reach.)
Whenever Thieving Magpie deals damage to an opponent, draw a card.

Deem Inferior

This spell costs {1} less to cast for each card you've drawn this turn.
The owner of target nonland permanent puts it into their library second from the top or on the bottom.

Festering Goblin

When Festering Goblin dies, target creature gets -1/-1 until end of turn.

Deep Analysis

Target player draws two cards.
Flashback—{1}{U}, Pay 3 life. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Peregrine Drake

Flying
When Peregrine Drake enters, untap up to five lands.

Impulse

Look at the top four cards of your library. Put one of them into your hand and the rest on the bottom of your library in any order.