Sea of Clouds

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

Rejuvenating Springs

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

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

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

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

{T}, Pay 1 life, Sacrifice Misty Rainforest: Search your library for a Forest or Island card, put it onto the battlefield, then shuffle.

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

({T}: Add {G} or {U}.)
As Breeding Pool enters, you may pay 2 life. If you don't, it enters tapped.