Morphic Pool

Morphic Pool enters tapped unless you have two or more opponents.
{T}: Add {U} or {B}.

Training Center

Training Center enters tapped unless you have two or more opponents.
{T}: Add {U} or {R}.

Sea of Clouds enters tapped unless you have two or more opponents.
{T}: Add {W} or {U}.

Undergrowth Stadium enters tapped unless you have two or more opponents.
{T}: Add {B} or {G}.

{T}: Add one mana of any type that a land you control could produce.

Spectator Seating enters tapped unless you have two or more opponents.
{T}: Add {R} or {W}.

Whenever City of Brass becomes tapped, it deals 1 damage to you.
{T}: Add one mana of any color.

{T}: Add one mana of any color.
Whenever you tap Forbidden Orchard for mana, target opponent creates a 1/1 colorless Spirit creature token.

Rejuvenating Springs enters tapped unless you have two or more opponents.
{T}: Add {G} or {U}.

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

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

Luxury Suite enters tapped unless you have two or more opponents.
{T}: Add {B} or {R}.

Vault of Champions enters tapped unless you have two or more opponents.
{T}: Add {W} or {B}.

Spire Garden enters tapped unless you have two or more opponents.
{T}: Add {R} or {G}.

Bountiful Promenade enters tapped unless you have two or more opponents.
{T}: Add {G} or {W}.