Mortivore

Mortivore's power and toughness are each equal to the number of creature cards in all graveyards.
{B}: Regenerate Mortivore.

Surge Mare

Surge Mare can't be blocked by green creatures.
Whenever Surge Mare deals damage to an opponent, you may draw a card. If you do, discard a card.
{1}{U}: Surge Mare gets +2/-2 until end of turn.

Jace's Phantasm

Flying
Jace's Phantasm gets +4/+4 as long as an opponent has ten or more cards in their graveyard.

Mirko Vosk, Mind Drinker

Flying
Whenever Mirko Vosk, Mind Drinker deals combat damage to a player, that player reveals cards from the top of their library until they reveal four land cards, then puts those cards into their graveyard.

Fleet Swallower

Whenever Fleet Swallower attacks, target player mills half their library, rounded up.

Consuming Aberration

Consuming Aberration's power and toughness are each equal to the number of cards in your opponents' graveyards.
Whenever you cast a spell, each opponent reveals cards from the top of their library until they reveal a land card, then puts those cards into their graveyard.