Sunken Hollow

({T}: Add {U} or {B}.)
Sunken Hollow enters tapped unless you control two or more basic lands.

Exotic Orchard

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

Swords to Plowshares

Exile target creature. Its controller gains life equal to its power.

Mistvault Bridge

Mistvault Bridge enters tapped.
Indestructible
{T}: Add {U} or {B}.

Arcane Signet

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

Azorius Signet

Vault of Whispers

Orzhov Signet

Solemn Simulacrum

When this creature enters, you may search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.
When this creature dies, you may draw a card.

Prairie Stream

({T}: Add {W} or {U}.)
Prairie Stream enters tapped unless you control two or more basic lands.

Seat of the Synod

Dimir Signet

Darksteel Citadel

Urza, Chief Artificer

Affinity for artifact creatures (This spell costs {1} less to cast for each artifact creature you control.)
Artifact creatures you control have menace.
At the beginning of your end step, create a 0/0 colorless Construct artifact creature token with "This creature gets +1/+1 for each artifact you control."

Ancient Den

Razortide Bridge

Razortide Bridge enters tapped.
Indestructible
{T}: Add {W} or {U}.

Sai, Master Thopterist

Whenever you cast an artifact spell, create a 1/1 colorless Thopter artifact creature token with flying.
{1}{U}, Sacrifice two artifacts: Draw a card.

Goldmire Bridge

Goldmire Bridge enters tapped.
Indestructible
{T}: Add {W} or {B}.

Command Tower

Transmutation Font

{T}: Create your choice of a Blood token, a Clue token, or a Food token.
{3}, {T}, Sacrifice three artifact tokens with different names: Search your library for an artifact card, put it onto the battlefield, then shuffle. Activate only as a sorcery.