Festerleech

Whenever Festerleech deals combat damage to a player, you mill two cards.
{1}{B}: Festerleech gets +2/+2 until end of turn. Activate only once each turn.

Desperate Bloodseeker

Lifelink
When Desperate Bloodseeker enters, target player mills two cards. (They put the top two cards of their library into their graveyard.)

Stubborn Burrowfiend

Whenever Stubborn Burrowfiend becomes saddled for the first time each turn, mill two cards, then Stubborn Burrowfiend gets +X/+X until end of turn, where X is the number of creature cards in your graveyard.
Saddle 2 (Tap any number of other creatures you control with total power 2 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)

Daggerfang Duo

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

Akawalli, the Seething Tower

Descend 4 — As long as there are four or more permanent cards in your graveyard, Akawalli, the Seething Tower gets +2/+2 and has trample.
Descend 8 — As long as there are eight or more permanent cards in your graveyard, Akawalli gets an additional +2/+2 and can't be blocked by more than one creature.

Screaming Phantom

Flying
Whenever Screaming Phantom attacks, mill a card. (Put the top card of your library into your graveyard.)

Rise of the Varmints

Create X 2/1 green Varmint creature tokens, where X is the number of creature cards in your graveyard.
Plot {2}{G} (You may pay {2}{G} and exile this card from your hand. Cast it as a sorcery on a later turn without paying its mana cost. Plot only as a sorcery.)

Forest

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.

Swamp

Huskburster Swarm

This spell costs {1} less to cast for each creature card you own in exile and in your graveyard.
Menace, deathtouch

Basking Capybara

Descend 4 — Basking Capybara gets +3/+0 as long as there are four or more permanent cards in your graveyard.

Echo of Dusk

Descend 4 — As long as there are four or more permanent cards in your graveyard, Echo of Dusk gets +1/+1 and has lifelink.

Join the Dead

Target creature gets -5/-5 until end of turn.
Descend 4 — That creature gets -10/-10 until end of turn instead if there are four or more permanent cards in your graveyard.