Oskar, Rubbish Reclaimer

This spell costs {1} less to cast for each different mana value among cards in your graveyard.
Whenever you discard a nonland card, you may cast it from your graveyard.

Ominous Roost

When this enchantment enters and whenever you cast a spell from your graveyard, create a 1/1 blue Bird creature token with flying and "This token can block only creatures with flying."

Sky Diamond

This artifact enters tapped.
{T}: Add {U}.

Faith of the Devoted

Whenever you cycle or discard a card, you may pay {1}. If you do, each opponent loses 2 life and you gain 2 life.

Security Bypass

Enchant creature
As long as enchanted creature is attacking alone, it can't be blocked.
Enchanted creature has "Whenever this creature deals combat damage to a player, it connives." (Its controller draws a card, then discards a card. If they discarded a nonland card, they put a +1/+1 counter on this creature.)

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice this artifact: Draw a card.

Secrets of the Dead

Whenever you cast a spell from your graveyard, draw a card.

Dimir Signet

The Underworld Cookbook

{T}, Discard a card: Create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this token: You gain 3 life.")
{4}, {T}, Sacrifice this artifact: Return target creature card from your graveyard to your hand.

Charcoal Diamond

This artifact enters tapped.
{T}: Add {B}.

All-Seeing Arbiter

Flying
Whenever this creature enters or attacks, draw two cards, then discard a card.
Whenever you discard a card, target creature an opponent controls gets -X/-0 until your next turn, where X is the number of different mana values among cards in your graveyard.

Collector's Vault

{2}, {T}: Draw a card, then discard a card. Create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Archfiend of Ifnir

Flying
Whenever you cycle or discard another card, put a -1/-1 counter on each creature your opponents control.
Cycling {2} ({2}, Discard this card: Draw a card.)

Syr Konrad, the Grim

Whenever another creature dies, or a creature card is put into a graveyard from anywhere other than the battlefield, or a creature card leaves your graveyard, Syr Konrad deals 1 damage to each opponent.
{1}{B}: Each player mills a card. (They each put the top card of their library into their graveyard.)

Sol Ring

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice this artifact: Draw a card.

Grimoire of the Dead

{1}, {T}, Discard a card: Put a study counter on Grimoire of the Dead.
{T}, Remove three study counters from Grimoire of the Dead and sacrifice it: Put all creature cards from all graveyards onto the battlefield under your control. They're black Zombies in addition to their other colors and types.

Dying to Serve

Whenever you discard one or more cards, create a tapped 2/2 black Zombie creature token. This ability triggers only once each turn.

Fluctuator

Cycling abilities you activate cost {2} less to activate.

Key to the City

{T}, Discard a card: Up to one target creature can't be blocked this turn.
Whenever this artifact becomes untapped, you may pay {2}. If you do, draw a card.

Feast of Sanity

Whenever you discard a card, this enchantment deals 1 damage to any target and you gain 1 life.

Prismatic Lens

{T}: Add {C}.
{1}, {T}: Add one mana of any color.

Drake Haven

Whenever you cycle or discard a card, you may pay {1}. If you do, create a 2/2 blue Drake creature token with flying.

Arcane Signet

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