Command Tower

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

Ziatora's Proving Ground

({T}: Add {B}, {R}, or {G}.)
This land enters tapped.
Cycling {3} ({3}, Discard this card: Draw a card.)

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

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
{T}: Add {B}, {R}, or {G}.

This land enters tapped.
{T}: Add {B}, {R}, or {G}.

Vigilance
A player losing unspent mana causes that player to lose that much life.
{1}, {T}: Each player adds {B}{R}{G}.