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.

Temple of Deceit

Temple of Deceit enters the battlefield tapped.
When Temple of Deceit enters the battlefield, scry 1.
{T}: Add {U} or {B}.

Careful Study

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.)

Rites of Refusal

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

Negate

Drowned Catacomb

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

Swamp

Island

Tormod's Crypt

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

Encrust

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

Tainted Isle

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

Chainer's Edict

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

Hero's Downfall

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.

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."

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."

Gloomdrifter

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

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.)

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."