Spectral Searchlight

{T}: Choose a player. That player adds one mana of any color they choose.

Eladamri's Vineyard

At the beginning of each player's first main phase, that player adds {G}{G}.

Mana Flare

Whenever a player taps a land for mana, that player adds one mana of any type that land produced.

Overabundance

Whenever a player taps a land for mana, that player adds one mana of any type that land produced, and Overabundance deals 1 damage to the player.

Yurlok of Scorch Thrash

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

Keeper of Progenitus

Whenever a player taps a Mountain, Forest, or Plains for mana, that player adds one mana of any type that land produced.

Blinkmoth Urn

At the beginning of each player's first main phase, if Blinkmoth Urn is untapped, that player adds {C} for each artifact they control.

Tangleroot

Whenever a player casts a creature spell, that player adds {G}.

Stadium Vendors

When Stadium Vendors enters, choose a player. That player adds two mana of any one color they choose.

Valleymaker

{T}, Sacrifice a Mountain: Valleymaker deals 3 damage to target creature.
{T}, Sacrifice a Forest: Choose a player. That player adds {G}{G}{G}.

Heartbeat of Spring

Shizuko, Caller of Autumn

At the beginning of each player's upkeep, that player adds {G}{G}{G}. Until end of turn, they don't lose this mana as steps and phases end.

Dictate of Karametra

Flash
Whenever a player taps a land for mana, that player adds one mana of any type that land produced.

Magus of the Vineyard

Bigger on the Inside

Enchant artifact or land
Enchanted permanent has "{T}: Target player adds two mana of any one color. The next spell they cast this turn has cascade." (When they cast their next spell, they exile cards from the top of their library until they exile a nonland card that costs less. They may cast it without paying its mana cost. They put the exiled cards on the bottom in a random order.)