Boneyard Wurm

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

Swamp

Spider Spawning

Create a 1/2 green Spider creature token with reach for each creature card in your graveyard.
Flashback {6}{B} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Mulch

Reveal the top four cards of your library. Put all land cards revealed this way into your hand and the rest into your graveyard.

Kessig Cagebreakers

Whenever Kessig Cagebreakers attacks, create a 2/2 green Wolf creature token that's tapped and attacking for each creature card in your graveyard.

Typhoid Rats

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)

Forest

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.