Maralen of the Mornsong

Players can't draw cards.
At the beginning of each player's draw step, that player loses 3 life, searches their library for a card, puts it into their hand, then shuffles.

Dark Sphere

{T}, Sacrifice this artifact: The next time a source of your choice would deal damage to you this turn, prevent half that damage, rounded down.

Exsanguinate

Each opponent loses X life. You gain life equal to the life lost this way.

Sol Ring

Thought Vessel

You have no maximum hand size.
{T}: Add {C}.

Opposition Agent

Flash
You control your opponents while they're searching their libraries.
While an opponent is searching their library, they exile each card they find. You may play those cards for as long as they remain exiled, and you may spend mana as though it were mana of any color to cast them.

Cabal Coffers

{2}, {T}: Add {B} for each Swamp you control.

Swamp

Cabal Ritual

Add {B}{B}{B}.
Threshold — Add {B}{B}{B}{B}{B} instead if there are seven or more cards in your graveyard.

Sickening Dreams

As an additional cost to cast this spell, discard X cards.
Sickening Dreams deals X damage to each creature and each player.

Everflowing Chalice

Multikicker {2} (You may pay an additional {2} any number of times as you cast this spell.)
This artifact enters with a charge counter on it for each time it was kicked.
{T}: Add {C} for each charge counter on this artifact.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Glacial Chasm

Cumulative upkeep—Pay 2 life. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
When this land enters, sacrifice a land.
Creatures you control can't attack.
Prevent all damage that would be dealt to you.

Skirge Familiar

Ad Nauseam

Reveal the top card of your library and put that card into your hand. You lose life equal to its mana value. You may repeat this process any number of times.