Haunted One

Commander creatures you own have "Whenever this creature becomes tapped, it and other creatures you control that share a creature type with it each get +2/+0 and gain undying until end of turn." (When a creature with undying dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)

Zulaport Cutthroat

Whenever this creature or another creature you control dies, each opponent loses 1 life and you gain 1 life.

Ellie, Brick Master

Distract the Horde — Whenever a player attacks one of your opponents, that attacking player creates a tapped 1/1 black Fungus Zombie creature token named Cordyceps Infected that's attacking that opponent.
Partner—Survivors (You can have two commanders if both have this ability.)

Braids, Arisen Nightmare

At the beginning of your end step, you may sacrifice an artifact, creature, enchantment, land, or planeswalker. If you do, each opponent may sacrifice a permanent of their choice that shares a card type with it. For each opponent who doesn't, that player loses 2 life and you draw a card.

Abby, Merciless Soldier

When you cast this spell, create a number of 1/1 black Fungus Zombie creature tokens named Cordyceps Infected equal to the amount of mana spent to cast it.
Abby enters under the control of an opponent of your choice.
Partner—Survivors (You can have two commanders if both have this ability.)

Saproling

Mycoloth

Devour 2 (As this creature enters, you may sacrifice any number of creatures. It enters with twice that many +1/+1 counters on it.)
At the beginning of your upkeep, create a 1/1 green Saproling creature token for each +1/+1 counter on this creature.

Ellie, Vengeful Hunter

Pay 2 life, Sacrifice another creature: Ellie deals 2 damage to target player and gains indestructible until end of turn.
Partner—Survivors (You can have two commanders if both have this ability.)

Cabal Ritual

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

Cordyceps Infected

Morbid Opportunist

Whenever one or more other creatures die, draw a card. This ability triggers only once each turn.

Blood Artist

Whenever this creature or another creature dies, target player loses 1 life and you gain 1 life.

Dictate of Erebos

Flash
Whenever a creature you control dies, each opponent sacrifices a creature of their choice.

Pitiless Plunderer

Whenever another creature you control dies, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Skullclamp

Equipped creature gets +1/-1.
Whenever equipped creature dies, draw two cards.
Equip {1}

Bastion of Remembrance

When this enchantment enters, create a 1/1 white Human Soldier creature token.
Whenever a creature you control dies, each opponent loses 1 life and you gain 1 life.

Joel, Resolute Survivor

Menace
Whenever a creature token dies, put a +1/+1 counter on Joel and draw a card. This ability triggers only once each turn.
Partner—Survivors (You can have two commanders if both have this ability.)