Cabal Ritual

Add {B}{B}{B}.
Threshold — Add {B}{B}{B}{B}{B} instead if seven or more cards are in your graveyard.

Lord of Extinction

Lord of Extinction's power and toughness are each equal to the number of cards in all graveyards.

Golgari Thug

When Golgari Thug dies, put target creature card from your graveyard on top of your library.
Dredge 4 (If you would draw a card, you may mill four cards instead. If you do, return this card from your graveyard to your hand.)

Krosan Beast

Threshold — Krosan Beast gets +7/+7 as long as seven or more cards are in your graveyard.

Body Snatcher

When Body Snatcher enters the battlefield, exile it unless you discard a creature card.
When Body Snatcher dies, exile Body Snatcher and return target creature card from your graveyard to the battlefield.

Archon of Falling Stars

Flying
When Archon of Falling Stars dies, you may return target enchantment card from your graveyard to the battlefield.

Necrosavant

{3}{B}{B}, Sacrifice a creature: Return Necrosavant from your graveyard to the battlefield. Activate only during your upkeep.

Hunting Grounds

Threshold — As long as seven or more cards are in your graveyard, Hunting Grounds has "Whenever an opponent casts a spell, you may put a creature card from your hand onto the battlefield."

Oversold Cemetery

At the beginning of your upkeep, if you have four or more creature cards in your graveyard, you may return target creature card from your graveyard to your hand.

Millikin

{T}, Mill a card: Add {C}. (To mill a card, put the top card of your library into your graveyard.)

Stitch Together

Return target creature card from your graveyard to your hand.
Threshold — Return that card from your graveyard to the battlefield instead if seven or more cards are in your graveyard.

Mystic Enforcer

Protection from black
Threshold — As long as seven or more cards are in your graveyard, Mystic Enforcer gets +3/+3 and has flying.

Karador, Ghost Chieftain

This spell costs {1} less to cast for each creature card in your graveyard.
Once during each of your turns, you may cast a creature spell from your graveyard.

Golgari Grave-Troll

Golgari Grave-Troll enters the battlefield with a +1/+1 counter on it for each creature card in your graveyard.
{1}, Remove a +1/+1 counter from Golgari Grave-Troll: Regenerate Golgari Grave-Troll.
Dredge 6 (If you would draw a card, you may mill six cards instead. If you do, return this card from your graveyard to your hand.)

Chlorophant

At the beginning of your upkeep, you may put a +1/+1 counter on Chlorophant.
Threshold — As long as seven or more cards are in your graveyard, Chlorophant has "At the beginning of your upkeep, you may put another +1/+1 counter on Chlorophant."

Grim Flayer

Trample
Whenever Grim Flayer deals combat damage to a player, surveil 3. (Look at the top three cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)
Delirium — Grim Flayer gets +2/+2 as long as there are four or more card types among cards in your graveyard.

Acolyte of Affliction

When Acolyte of Affliction enters the battlefield, mill two cards, then you may return a permanent card from your graveyard to your hand.

Deadbridge Chant

When Deadbridge Chant enters the battlefield, mill ten cards.
At the beginning of your upkeep, choose a card at random in your graveyard. If it's a creature card, put it onto the battlefield. Otherwise, put it into your hand.

Ancestral Tribute

You gain 2 life for each card in your graveyard.
Flashback {9}{W}{W}{W} (You may cast this card from your graveyard for its flashback cost. Then exile it.)