Fertile Ground

Enchant land
Whenever enchanted land is tapped for mana, its controller adds an additional one mana of any color.

Carpet of Flowers

At the beginning of each of your main phases, if you haven't added mana with this ability this turn, you may add X mana of any one color, where X is the number of Islands target opponent controls.

Arcane Signet

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

Moss Diamond

Moss Diamond enters tapped.
{T}: Add {G}.

Sol Ring

Utopia Sprawl

Enchant Forest
As Utopia Sprawl enters, choose a color.
Whenever enchanted Forest is tapped for mana, its controller adds an additional one mana of the chosen color.

Kosei, Penitent Warlord

As long as Kosei, Penitent Warlord is enchanted, equipped, and has a counter on it, Kosei has "Whenever Kosei, Penitent Warlord deals combat damage to an opponent, you draw that many cards and Kosei deals that much damage to each other opponent."