Manabarbs

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

Seeker of Skybreak

Stoneshaker Shaman

At the beginning of each player's end step, that player sacrifices an untapped land of their choice.

Cultivate

Search your library for up to two basic land cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Tyvar, Jubilant Brawler

You may activate abilities of creatures you control as though those creatures had haste.
+1: Untap up to one target creature.
−2: Mill three cards, then you may return a creature card with mana value 2 or less from your graveyard to the battlefield.

Rampant Growth

Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Victory Chimes

Untap Victory Chimes during each other player's untap step.
{T}: A player of your choice adds {C}.

Horizon Stone

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

Rug of Smothering

Flying
Whenever a player casts a spell, they lose 1 life for each spell they've cast this turn.

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}.

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.)

Zhur-Taa Druid

{T}: Add {G}.
Whenever you tap Zhur-Taa Druid for mana, it deals 1 damage to each opponent.

Kaervek the Merciless

Whenever an opponent casts a spell, Kaervek the Merciless deals damage equal to that spell's mana value to any target.

Heartbeat of Spring

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

Zhur-Taa Ancient

Goblin Anarchomancer

Each spell you cast that's red or green costs {1} less to cast.

Llanowar Elves

Lavalanche

Lavalanche deals X damage to target player or planeswalker and each creature that player or that planeswalker's controller controls.