Gloomdrifter

Flying
Threshold — As long as seven or more cards are in your graveyard, Gloomdrifter has "When Gloomdrifter enters, nonblack creatures get -2/-2 until end of turn."

Temple of Deceit

This land enters tapped.
When this land enters, scry 1. (Look at the top card of your library. You may put that card on the bottom.)
{T}: Add {U} or {B}.

Decaying Soil

At the beginning of your upkeep, exile a card from your graveyard.
Threshold — As long as seven or more cards are in your graveyard, Decaying Soil has "Whenever a nontoken creature is put into your graveyard from the battlefield, you may pay {1}. If you do, return that card to your hand."

Careful Study

Tormod's Crypt

{T}, Sacrifice Tormod's Crypt: Exile target player's graveyard.

Bloodcurdler

Flying
At the beginning of your upkeep, mill a card.
Threshold — As long as seven or more cards are in your graveyard, Bloodcurdler gets +1/+1 and has "At the beginning of your end step, exile two cards from your graveyard."

Toxic Stench

Target nonblack creature gets -1/-1 until end of turn.
Threshold — If seven or more cards are in your graveyard, instead destroy that creature. It can't be regenerated.

Rites of Refusal

Discard any number of cards. Counter target spell unless its controller pays {3} for each card discarded this way.

Island

Deep Analysis

Target player draws two cards.
Flashback—{1}{U}, Pay 3 life. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Encrust

Enchant artifact or creature
Enchanted permanent doesn't untap during its controller's untap step and its activated abilities can't be activated.

Possessed Aven

Flying
Threshold — As long as seven or more cards are in your graveyard, Possessed Aven gets +1/+1, is black, and has "{2}{B}, {T}: Destroy target blue creature."

Tainted Isle

{T}: Add {C}.
{T}: Add {U} or {B}. Activate only if you control a Swamp.

Think Tank

At the beginning of your upkeep, surveil 1. (Look at the top card of your library. You may put that card into your graveyard.)

Swamp

Hero's Downfall

Drowned Catacomb

Drowned Catacomb enters tapped unless you control an Island or a Swamp.
{T}: Add {U} or {B}.

Negate

Chainer's Edict

Target player sacrifices a creature of their choice.
Flashback {5}{B}{B} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Putrid Imp

Discard a card: Putrid Imp gains flying until end of turn.
Threshold — As long as seven or more cards are in your graveyard, Putrid Imp gets +1/+1 and can't block.