Kaito, Bane of Nightmares

Ninjutsu {1}{U}{B} ({1}{U}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
During your turn, as long as Kaito has one or more loyalty counters on him, he's a 3/4 Ninja creature and has hexproof.
+1: You get an emblem with "Ninjas you control get +1/+1."
0: Surveil 2. Then draw a card for each opponent who lost life this turn.
−2: Tap target creature. Put two stun counters on it.

Swamp

Dashing Bloodsucker

Eerie — Whenever an enchantment you control enters and whenever you fully unlock a Room, Dashing Bloodsucker gets +2/+0 and gains lifelink until end of turn.

Give In to Violence

Target creature gets +2/+2 and gains lifelink until end of turn.

Cracked Skull

Enchant creature
When Cracked Skull enters, look at target player's hand. You may choose a nonland card from it. That player discards that card.
When enchanted creature is dealt damage, destroy it.

Stalked Researcher

Defender
Eerie — Whenever an enchantment you control enters and whenever you fully unlock a Room, Stalked Researcher can attack this turn as though it didn't have defender.

Terramorphic Expanse

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

Cackling Slasher

Deathtouch
Cackling Slasher enters with a +1/+1 counter on it if a creature died this turn.

Ghostly Keybearer

Flying
Whenever Ghostly Keybearer deals combat damage to a player, unlock a locked door of up to one target Room you control.

Floodpits Drowner

Flash
Vigilance
When Floodpits Drowner enters, tap target creature an opponent controls and put a stun counter on it.
{1}{U}, {T}: Shuffle Floodpits Drowner and target creature with a stun counter on it into their owners' libraries.

Nowhere to Run

Flash
When Nowhere to Run enters, target creature an opponent controls gets -3/-3 until end of turn.
Creatures your opponents control can be the targets of spells and abilities as though they didn't have hexproof. Ward abilities of those creatures don't trigger.

Clammy Prowler

Whenever Clammy Prowler attacks, another target attacking creature can't be blocked this turn.

Sporogenic Infection

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

Murder

Island

Final Vengeance

As an additional cost to cast this spell, sacrifice a creature or enchantment.
Exile target creature.

Fear of Impostors

Flash
When Fear of Impostors enters, counter target spell. Its controller manifests dread. (That player looks at the top two cards of their library, then puts one onto the battlefield face down as a 2/2 creature and the other into their graveyard. If it's a creature card, it can be turned face up any time for its mana cost.)

Creeping Peeper

{T}: Add {U}. Spend this mana only to cast an enchantment spell, unlock a door, or turn a permanent face up.