Grasping Scoundrel

This creature gets +1/+0 as long as it's attacking.

Jet Medallion

Black spells you cast cost {1} less to cast.

Swamp

Sengir, the Dark Baron

Flying
Whenever another creature dies, put two +1/+1 counters on Sengir.
Whenever another player loses the game, you gain life equal to that player's life total as the turn began.
Partner (You can have two commanders if both have partner.)

Knight of Infamy

Protection from white (This creature can't be blocked, targeted, dealt damage, or enchanted by anything white.)
Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)

Cathedral of War

This land enters tapped.
Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
{T}: Add {C}.

Ancestral Vengeance

Enchant creature
When this Aura enters, put a +1/+1 counter on target creature you control.
Enchanted creature gets -1/-1.

Astarion's Thirst

Exile target creature. Put X +1/+1 counters on a commander creature you control, where X is the power of the creature exiled this way.

Adorned Crocodile

When this creature dies, create a 2/2 black Zombie Druid creature token.
Renew — {B}, Exile this card from your graveyard: Put a +1/+1 counter on target creature. Activate only as a sorcery.

Reckoner Shakedown

Target opponent reveals their hand. You may choose a nonland card from it. If you do, that player discards that card. If you don't, put two +1/+1 counters on a creature or Vehicle you control.

Animal Sanctuary

{T}: Add {C}.
{2}, {T}: Put a +1/+1 counter on target Bird, Cat, Dog, Goat, Ox, or Snake.

Deadeye Tracker

{1}{B}, {T}: Exile two target cards from an opponent's graveyard. This creature explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

Fain, the Broker

{T}, Sacrifice a creature: Put two +1/+1 counters on target creature.
{T}, Remove a counter from a creature you control: Create a Treasure token.
{T}, Sacrifice an artifact: Create a 2/1 white and black Inkling creature token with flying.
{3}{B}: Untap Fain.

Yawgmoth, Thran Physician

Protection from Humans
Pay 1 life, Sacrifice another creature: Put a -1/-1 counter on up to one target creature and draw a card.
{B}{B}, Discard a card: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Essence Infusion

Put two +1/+1 counters on target creature. It gains lifelink until end of turn.

Iron Bully

Menace (This creature can't be blocked except by two or more creatures.)
When this creature enters, put a +1/+1 counter on target creature.

Retribution of the Ancients

{B}, Remove X +1/+1 counters from among creatures you control: Target creature gets -X/-X until end of turn.

Ent-Draught Basin

{X}, {T}: Put a +1/+1 counter on target creature with power X. Activate only as a sorcery.

Grave Strength

Choose target creature. Mill three cards, then put a +1/+1 counter on that creature for each creature card in your graveyard. (To mill three cards, put the top three cards of your library into your graveyard.)

Duty-Bound Dead

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
{3}{B}: Regenerate this creature. (The next time this creature would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)

Pip-Boy 3000

Whenever equipped creature attacks, choose one —
• Sort Inventory — Draw a card, then discard a card.
• Pick a Perk — Put a +1/+1 counter on that creature.
• Check Map — Untap up to two target lands.
Equip {2}

Dusk Sight

Put a +1/+1 counter on up to one target creature. Draw a card. (Then shuffle this card into its owner's library.)

Feral Deathgorger

Flying, deathtouch
When this creature enters, exile up to two target cards from a single graveyard.

Feral Deathgorger // Dusk Sight

Myr Scrapling

Sacrifice this creature: Put a +1/+1 counter on target creature.

Hagra Constrictor

This creature enters with two +1/+1 counters on it.
Each creature you control with a +1/+1 counter on it has menace. (A creature with menace can't be blocked except by two or more creatures.)

Greedy Freebooter

When this creature dies, scry 1 and create a Treasure token. (To scry 1, look at the top card of your library. You may put that card on the bottom. A Treasure token is an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Francisco, Fowl Marauder

Flying
Francisco can't block.
Whenever one or more Pirates you control deal damage to a player, Francisco explores.
Partner (You can have two commanders if both have partner.)

Servant of Nefarox

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)

Cannibalize

Choose two target creatures controlled by the same player. Exile one of those creatures and put two +1/+1 counters on the other.

Expanded Anatomy

Put two +1/+1 counters on target creature. It gains vigilance until end of turn.

Agent of the Shadow Thieves

Commander creatures you own have "Whenever this creature attacks a player, if no opponent has more life than that player, put a +1/+1 counter on this creature. It gains deathtouch and indestructible until end of turn."