Boneyard Wurm

Boneyard Wurm's power and toughness are each equal to the number of creature cards in your graveyard.

Nyx Weaver

Reach
At the beginning of your upkeep, mill two cards.
{1}{B}{G}, Exile Nyx Weaver: Return target card from your graveyard to your hand.

Nighthowler

Bestow {2}{B}{B} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
Nighthowler and enchanted creature each get +X/+X, where X is the number of creature cards in all graveyards.

Brawn

Trample
As long as Brawn is in your graveyard and you control a Forest, creatures you control have trample.

Terror Tide

Fathomless descent — All creatures get -X/-X until end of turn, where X is the number of permanent cards in your graveyard.

Splinterfright

Trample
Splinterfright's power and toughness are each equal to the number of creature cards in your graveyard.
At the beginning of your upkeep, mill two cards.

Grisly Salvage

Reveal the top five cards of your library. You may put a creature or land card from among them into your hand. Put the rest into your graveyard.

Lhurgoyf

Lhurgoyf's power is equal to the number of creature cards in all graveyards and its toughness is equal to that number plus 1.

Jarad, Golgari Lich Lord

Jarad, Golgari Lich Lord gets +1/+1 for each creature card in your graveyard.
{1}{B}{G}, Sacrifice another creature: Each opponent loses life equal to the sacrificed creature's power.
Sacrifice a Swamp and a Forest: Return Jarad from your graveyard to your hand.

Glowspore Shaman

When Glowspore Shaman enters the battlefield, mill three cards. You may put a land card from your graveyard on top of your library. (To mill a card, put the top card of your library into your graveyard.)

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.

Bonehoard

Living weapon (When this Equipment enters the battlefield, create a 0/0 black Phyrexian Germ creature token, then attach this to it.)
Equipped creature gets +X/+X, where X is the number of creature cards in all graveyards.
Equip {2}

Deathbloom Ritualist

{T}: Add X mana of any one color, where X is the number of creature cards in your graveyard.