Rashmi and Ragavan

Whenever you cast your first spell during each of your turns, exile the top card of target opponent's library and create a Treasure token. Then you may cast the exiled card without paying its mana cost if it's a spell with mana value less than the number of artifacts you control. If you don't cast it this way, you may cast it this turn.

Mishra's Bauble

{T}, Sacrifice this artifact: Look at the top card of target player's library. Draw a card at the beginning of the next turn's upkeep.

Arcane Signet

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

Sol Ring

Mox Opal

Metalcraft — {T}: Add one mana of any color. Activate only if you control three or more artifacts.