Helga, Skittish Seer

Whenever you cast a creature spell with mana value 4 or greater, you draw a card, gain 1 life, and put a +1/+1 counter on Helga.
{T}: Add X mana of any one color, where X is Helga's power. Spend this mana only to cast creature spells with mana value 4 or greater or creature spells with {X} in their mana costs.

Clement, the Worrywort

Vigilance
Whenever Clement or another creature you control enters, return up to one target creature you control with lesser mana value to its owner's hand.
Frogs you control have "{T}: Add {G} or {U}. Spend this mana only to cast a creature spell."

Fellwar Stone

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

Sol Ring

Grolnok, the Omnivore

Whenever a Frog you control attacks, mill three cards.
Whenever a permanent card is put into your graveyard from your library, exile it with a croak counter on it.
You may play lands and cast spells from among cards you own in exile with croak counters on them.

Command Tower

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

Arcane Signet

Temple of the False God

{T}: Add {C}{C}. Activate only if you control five or more lands.

Exotic Orchard

Command Bridge

This land enters tapped.
When this land enters, sacrifice it unless you tap an untapped permanent you control.
{T}: Add one mana of any color.