Harbinger of Night

At the beginning of your upkeep, put a -1/-1 counter on each creature.

Giant Oyster

You may choose not to untap Giant Oyster during your untap step.
{T}: For as long as Giant Oyster remains tapped, target tapped creature doesn't untap during its controller's untap step, and at the beginning of each of your draw steps, put a -1/-1 counter on that creature. When Giant Oyster leaves the battlefield or becomes untapped, remove all -1/-1 counters from the creature.

Nest of Scarabs

Whenever you put one or more -1/-1 counters on a creature, create that many 1/1 black Insect creature tokens.

Horobi, Death's Wail

Flying
Whenever a creature becomes the target of a spell or ability, destroy that creature.

Cerulean Wisps

Target creature becomes blue until end of turn. Untap that creature.
Draw a card.

Cowardice

Whenever a creature becomes the target of a spell or ability, return that creature to its owner's hand. (It won't be affected by the spell or ability.)

Dusk Urchins

Whenever Dusk Urchins attacks or blocks, put a -1/-1 counter on it.
When Dusk Urchins dies, draw a card for each -1/-1 counter on it.

Grave Betrayal

Whenever a creature you don't control dies, return it to the battlefield under your control with an additional +1/+1 counter on it at the beginning of the next end step. That creature is a black Zombie in addition to its other colors and types.

Underworld Connections

Enchant land
Enchanted land has "{T}, Pay 1 life: Draw a card."

Tidewater Minion

Defender (This creature can't attack.)
{4}: Tidewater Minion loses defender until end of turn.
{T}: Untap target permanent.

Contagion

You may pay 1 life and exile a black card from your hand rather than pay this spell's mana cost.
Distribute two -2/-1 counters among one or two target creatures.

Ring of Xathrid

{2}: Regenerate equipped creature. (The next time that creature would be destroyed this turn, it isn't. Instead tap it, remove all damage from it, and remove it from combat.)
At the beginning of your upkeep, put a +1/+1 counter on equipped creature if it's black.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Willbreaker

Whenever a creature an opponent controls becomes the target of a spell or ability you control, gain control of that creature for as long as you control Willbreaker.

Skeleton Ship

When you control no Islands, sacrifice Skeleton Ship.
{T}: Put a -1/-1 counter on target creature.

Power Conduit

{T}, Remove a counter from a permanent you control: Choose one —
• Put a charge counter on target artifact.
• Put a +1/+1 counter on target creature.

Virulent Wound

Put a -1/-1 counter on target creature. When that creature dies this turn, its controller gets a poison counter.

Leech Bonder

Leech Bonder enters with two -1/-1 counters on it.
{U}, {Q}: Move a counter from target creature onto a second target creature. ({Q} is the untap symbol.)

Dismiss into Dream

Each creature your opponents control is an Illusion in addition to its other types and has "When this creature becomes the target of a spell or ability, sacrifice it."

Vedalken Anatomist

{2}{U}, {T}: Put a -1/-1 counter on target creature. You may tap or untap that creature.

Serrated Arrows

Serrated Arrows enters with three arrowhead counters on it.
At the beginning of your upkeep, if there are no arrowhead counters on Serrated Arrows, sacrifice it.
{T}, Remove an arrowhead counter from Serrated Arrows: Put a -1/-1 counter on target creature.