Stalactite Stalker

Menace
At the beginning of your end step, if you descended this turn, put a +1/+1 counter on Stalactite Stalker. (You descended if a permanent card was put into your graveyard from anywhere.)
{2}{B}, Sacrifice Stalactite Stalker: Target creature gets -X/-X until end of turn, where X is Stalactite Stalker's power.

Undead Butler

When Undead Butler enters the battlefield, mill three cards. (Put the top three cards of your library into your graveyard.)
When Undead Butler dies, you may exile it. When you do, return target creature card from your graveyard to your hand.

Bloodtithe Harvester

When Bloodtithe Harvester enters the battlefield, create a Blood token. (It's an artifact with "{1}, {T}, Discard a card, Sacrifice this artifact: Draw a card.")
{T}, Sacrifice Bloodtithe Harvester: Target creature gets -X/-X until end of turn, where X is twice the number of Blood tokens you control. Activate only as a sorcery.

Takenuma, Abandoned Mire

{T}: Add {B}.
Channel — {3}{B}, Discard Takenuma, Abandoned Mire: Mill three cards, then return a creature or planeswalker card from your graveyard to your hand. This ability costs {1} less to activate for each legendary creature you control.

Snarling Gorehound

Menace
Whenever another creature with power 2 or less enters the battlefield under your control, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Swamp

Inti, Seneschal of the Sun

Whenever you attack, you may discard a card. When you do, put a +1/+1 counter on target attacking creature. It gains trample until end of turn.
Whenever you discard one or more cards, exile the top card of your library. You may play that card until your next end step.

Deathcap Marionette

Deathtouch
When Deathcap Marionette enters the battlefield, you may mill two cards. (You may put the top two cards of your library into your graveyard.)

Blood Spatter Analysis

When Blood Spatter Analysis enters the battlefield, it deals 3 damage to target creature an opponent controls.
Whenever one or more creatures die, mill a card and put a bloodstain counter on Blood Spatter Analysis. Then sacrifice it if it has five or more bloodstain counters on it. When you do, return target creature card from your graveyard to your hand.

The Grim Captain

Menace, trample, lifelink, hexproof
Whenever The Grim Captain attacks, each opponent sacrifices a nonland permanent. Then you may put an exiled creature card used to craft The Grim Captain onto the battlefield under your control tapped and attacking.

Throne of the Grim Captain

{T}: Mill two cards.
Craft with a Dinosaur, a Merfolk, a Pirate, and a Vampire {4} ({4}, Exile this artifact, Exile the four from among permanents you control and/or cards in your graveyard: Return this card transformed under its owner's control. Craft only as a sorcery.)

Throne of the Grim Captain // The Grim Captain

Deep-Cavern Bat

Flying, lifelink
When Deep-Cavern Bat enters the battlefield, look at target opponent's hand. You may exile a nonland card from it until Deep-Cavern Bat leaves the battlefield.

Burn Together

Target creature you control deals damage equal to its power to any other target. Then sacrifice it.

Callous Sell-Sword

Callous Sell-Sword enters the battlefield with a +1/+1 counter on it for each creature that died under your control this turn.

Callous Sell-Sword // Burn Together

Mountain

Souls of the Lost

As an additional cost to cast this spell, discard a card or sacrifice a permanent.
Fathomless descent — Souls of the Lost's power is equal to the number of permanent cards in your graveyard and its toughness is equal to that number plus 1.

Gnawing Vermin

When Gnawing Vermin enters the battlefield, target player mills two cards.
When Gnawing Vermin dies, target creature you don't control gets -1/-1 until end of turn.