Drown in the Loch

Choose one —
• Counter target spell with mana value less than or equal to the number of cards in its controller's graveyard.
• Destroy target creature with mana value less than or equal to the number of cards in its controller's graveyard.

Soaring Thought-Thief

Flash
Flying
As long as an opponent has eight or more cards in their graveyard, Rogues you control get +1/+0.
Whenever one or more Rogues you control attack, each opponent mills two cards.

Merfolk Windrobber

Flying
Whenever Merfolk Windrobber deals combat damage to a player, that player mills a card. (They put the top card of their library into their graveyard.)
Sacrifice Merfolk Windrobber: Draw a card. Activate only if an opponent has eight or more cards in their graveyard.

Into the Story

This spell costs {3} less to cast if an opponent has seven or more cards in their graveyard.
Draw four cards.

Malakir Mire

Malakir Mire enters tapped.
{T}: Add {B}.

Malakir Rebirth

Choose target creature. You lose 2 life. Until end of turn, that creature gains "When this creature dies, return it to the battlefield tapped under its owner's control."

Malakir Rebirth // Malakir Mire

Swamp

Power Word Kill

Destroy target non-Angel, non-Demon, non-Devil, non-Dragon creature.

Sunken Hollow

({T}: Add {U} or {B}.)
Sunken Hollow enters tapped unless you control two or more basic lands.

Crippling Fear

Choose a creature type. Creatures that aren't of the chosen type get -3/-3 until end of turn.

Thieves' Guild Enforcer

Flash
Whenever Thieves' Guild Enforcer or another Rogue you control enters, each opponent mills two cards.
As long as an opponent has eight or more cards in their graveyard, Thieves' Guild Enforcer gets +2/+1 and has deathtouch.

Bloodchief's Thirst

Kicker {2}{B} (You may pay an additional {2}{B} as you cast this spell.)
Destroy target creature or planeswalker with mana value 2 or less. If this spell was kicked, instead destroy target creature or planeswalker.