Festering Goblin

When Festering Goblin dies, target creature gets -1/-1 until end of turn.

Sivriss, Nightmare Speaker

{T}, Sacrifice another creature or an artifact: For each opponent, you mill a card, then return that card from your graveyard to your hand unless that player pays 3 life. (To mill a card, put the top card of your library into your graveyard.)
Choose a Background (You can have a Background as a second commander.)

Black Cat

When Black Cat dies, target opponent discards a card at random.

Gurmag Angler

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)

Myr Moonvessel

Grim Physician

When Grim Physician dies, target creature an opponent controls gets -1/-1 until end of turn.

Perilous Myr

When Perilous Myr dies, it deals 2 damage to any target.

Elvish Doomsayer

When Elvish Doomsayer dies, each opponent discards a card.

Zephyr Winder

Flying
Whenever Zephyr Winder deals combat damage to a player, untap up to one target creature.

Vizier of Tumbling Sands

{T}: Untap another target permanent.
Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)
When you cycle Vizier of Tumbling Sands, untap target permanent.

Shambling Goblin

When Shambling Goblin dies, target creature an opponent controls gets -1/-1 until end of turn.

Doomed Dissenter

When Doomed Dissenter dies, create a 2/2 black Zombie creature token.

Lotleth Giant

Undergrowth — When Lotleth Giant enters, it deals 1 damage to target opponent for each creature card in your graveyard.

Hand of Emrakul

You may sacrifice four Eldrazi Spawn rather than pay this spell's mana cost.
Annihilator 1 (Whenever this creature attacks, defending player sacrifices a permanent of their choice.)

Sultai Emissary

When Sultai Emissary dies, manifest the top card of your library. (Put that card onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)

Abyssal Gatekeeper

When Abyssal Gatekeeper dies, each player sacrifices a creature of their choice.

Gloom Sower

Whenever Gloom Sower becomes blocked by a creature, that creature's controller loses 2 life and you gain 2 life.

Nested Shambler

When Nested Shambler dies, create X tapped 1/1 green Squirrel creature tokens, where X is Nested Shambler's power.

Demonic Stench

Each creature that blocked this turn gets -1/-1 until end of turn. (Then exile this card. You may cast the creature later from exile.)

Hezrou

Whenever one or more creatures you control become blocked, each blocking creature gets -1/-1 until end of turn.

Hezrou // Demonic Stench

Ulamog's Crusher

Annihilator 2 (Whenever this creature attacks, defending player sacrifices two permanents of their choice.)
Ulamog's Crusher attacks each combat if able.

Drainpipe Vermin

When Drainpipe Vermin dies, you may pay {B}. If you do, target player discards a card.

Writhing Necromass

This spell costs {1} less to cast for each creature card in your graveyard.
Deathtouch

Scion of Halaster

Commander creatures you own have "The first time you would draw a card each turn, instead look at the top two cards of your library. Put one of them into your graveyard and the other back on top of your library. Then draw a card."

Eldrazi Devastator

Sparring Construct

When Sparring Construct dies, put a +1/+1 counter on target creature you control.

Festering Mummy

When Festering Mummy dies, you may put a -1/-1 counter on target creature.

Nezumi Linkbreaker

When Nezumi Linkbreaker dies, create a 1/1 red Mercenary creature token with "{T}: Target creature you control gets +1/+0 until end of turn. Activate only as a sorcery."

Deathgreeter

Whenever another creature dies, you may gain 1 life.

Shambling Ghast

When Shambling Ghast dies, choose one —
• Target creature an opponent controls gets -1/-1 until end of turn.
• Create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Freed from the Real

Enchant creature
{U}: Tap enchanted creature.
{U}: Untap enchanted creature.

Galvanic Alchemist

Soulbond (You may pair this creature with another unpaired creature when either enters. They remain paired for as long as you control both of them.)
As long as Galvanic Alchemist is paired with another creature, each of those creatures has "{2}{U}: Untap this creature."

Nimbleclaw Adept

Bigby's Hand — {T}: Untap two other target permanents. Activate only as a sorcery and only once each turn.

Stonybrook Angler

{1}{U}, {T}: You may tap or untap target creature.

Greedy Freebooter

When Greedy Freebooter 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 artifact: Add one mana of any color.")