Typhoid Rats

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)

Graf Rats

At the beginning of combat on your turn, if you both own and control Graf Rats and a creature named Midnight Scavengers, exile them, then meld them into Chittering Host.

Terror

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

Dogged Pursuit

At the beginning of your end step, each opponent loses 1 life and you gain 1 life.

Professor's Warning

Choose one —
• Put a +1/+1 counter on target creature.
• Target creature gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)

Guildsworn Prowler

Deathtouch
When Guildsworn Prowler dies, if it wasn't blocking, draw a card.

Atrocious Experiment

Target player mills two cards, draws two cards, and loses 2 life. (To mill a card, a player puts the top card of their library into their graveyard.)

Rush of Vitality

Target creature gets +1/+0 and gains lifelink and indestructible until end of turn. (Damage dealt by that creature also causes its controller to gain that much life, and it can't be destroyed by damage or effects that say "destroy.")

Unearth

Return target creature card with mana value 3 or less from your graveyard to the battlefield.
Cycling {2} ({2}, Discard this card: Draw a card.)

Aspect of Lamprey

Enchant creature you control
When Aspect of Lamprey enters the battlefield, target opponent discards two cards.
Enchanted creature has lifelink.

Fake Your Own Death

Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield tapped under its owner's control and you create a Treasure token." (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Sign in Blood

Target player draws two cards and loses 2 life.

Midnight Scavengers

When Midnight Scavengers enters the battlefield, you may return target creature card with mana value 3 or less from your graveyard to your hand.
(Melds with Graf Rats.)

Contaminated Ground

Enchant land
Enchanted land is a Swamp.
Whenever enchanted land becomes tapped, its controller loses 2 life.

Battlefly Swarm

Flying
{B}: Battlefly Swarm gains deathtouch until end of turn.

Tragic Fall

Target creature gets -3/-3 until end of turn.
Hellbent — That creature gets -13/-13 until end of turn instead if you have no cards in hand.

Swamp

Sunscorched Desert

When Sunscorched Desert enters the battlefield, it deals 1 damage to target player or planeswalker.
{T}: Add {C}.