Arcane Signet

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

Hedron Crab

Landfall — Whenever a land you control enters, target player mills three cards. (They put the top three cards of their library into their graveyard.)

Can't Wake Up

Target player mills four cards. (Then exile this card. You may cast the creature later from exile.)

Cruel Somnophage

Cruel Somnophage's power and toughness are each equal to the number of creature cards in all graveyards.

Cruel Somnophage // Can't Wake Up

Nighthowler

Bestow {2}{B}{B} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
This creature and enchanted creature each get +X/+X, where X is the number of creature cards in all graveyards.

Bruvac the Grandiloquent

If an opponent would mill one or more cards, they mill twice that many cards instead. (To mill a card, a player puts the top card of their library into their graveyard.)

Mesmeric Orb

Whenever a permanent becomes untapped, that permanent's controller mills a card.

Gogo, Master of Mimicry

{X}{X}, {T}: Copy target activated or triggered ability you control X times. You may choose new targets for the copies. This ability can't be copied and X can't be 0. (Mana abilities can't be targeted.)

Lotus Petal

{T}, Sacrifice this artifact: Add one mana of any color.

Consuming Aberration

Consuming Aberration's power and toughness are each equal to the number of cards in your opponents' graveyards.
Whenever you cast a spell, each opponent reveals cards from the top of their library until they reveal a land card, then puts those cards into their graveyard.

Drown in the Loch

Choose one —
• Counter target spell with mana value less than or equal to the number of cards in its controller's graveyard.
• Destroy target creature with mana value less than or equal to the number of cards in its controller's graveyard.

Mindcrank

Whenever an opponent loses life, that player mills that many cards. (Damage causes loss of life.)

Charix, the Raging Isle

Spells your opponents cast that target Charix cost {2} more to cast.
{3}: Charix gets +X/-X until end of turn, where X is the number of Islands you control.

Phenax, God of Deception

Indestructible
As long as your devotion to blue and black is less than seven, Phenax isn't a creature.
Creatures you control have "{T}: Target player mills X cards, where X is this creature's toughness."

Fellwar Stone

{T}: Add one mana of any color that a land an opponent controls could produce.

Sol Ring

Ruin Crab

Landfall — Whenever a land you control enters, each opponent mills three cards. (To mill a card, a player puts the top card of their library into their graveyard.)

Tree of Perdition

Defender
{T}: Exchange target opponent's life total with this creature's toughness.