Arcane Signet

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

Barbflare Gremlin

First strike, haste
Whenever a player taps a land for mana, if Barbflare Gremlin is tapped, that player adds one mana of any type that land produced. Then that land deals 1 damage to that player.

Heartbeat of Spring

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

Manabarbs

Whenever a player taps a land for mana, Manabarbs deals 1 damage to that player.

Command Tower

Forest

Zhur-Taa Ancient

Mana Flare

Citadel of Pain

At the beginning of each player's end step, Citadel of Pain deals X damage to that player, where X is the number of untapped lands they control.

Reliquary Tower

You have no maximum hand size.
{T}: Add {C}.

Mountain

Horizon Stone

If you would lose unspent mana, that mana becomes colorless instead.

Sol Ring

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.

Swamp

Belbe, Corrupted Observer

At the beginning of each postcombat main phase, the active player adds {C}{C} for each of your opponents who lost life this turn. (Damage causes loss of life.)

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}.