Ramos, Dragon Engine

Flying
Whenever you cast a spell, put a +1/+1 counter on Ramos for each of that spell's colors.
Remove five +1/+1 counters from Ramos: Add {W}{W}{U}{U}{B}{B}{R}{R}{G}{G}. Activate only once each turn.

Fellwar Stone

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

Burgeoning

Whenever an opponent plays a land, you may put a land card from your hand onto the battlefield.

Sol Ring

Arcane Signet

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