Fellwar Stone

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

Darksteel Monolith

Indestructible
Once each turn, you may pay {0} rather than pay the mana cost for a colorless spell you cast from your hand.

Azorius Signet

Orzhov Signet

Talisman of Dominance

{T}: Add {C}.
{T}: Add {U} or {B}. Talisman of Dominance deals 1 damage to you.

Arcane Signet

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

Seat of the Synod

Vault of Whispers

Sydri, Galvanic Genius

{U}: Target noncreature artifact becomes an artifact creature with power and toughness each equal to its mana value until end of turn.
{W}{B}: Target artifact creature gains deathtouch and lifelink until end of turn.