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}.

Citadel of Pain

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

Mana Short

Tap all lands target player controls and that player loses all unspent mana.

Well of Life

At the beginning of your end step, if you control no untapped lands, you gain 2 life.

Nantuko Shaman

When this creature enters, if you control no tapped lands, draw a card.
Suspend 1—{2}{G}{G} (Rather than cast this card from your hand, you may pay {2}{G}{G} and exile it with a time counter on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost. It has haste.)

Drain Power

Target player activates a mana ability of each land they control. Then that player loses all unspent mana and you add the mana lost this way.

Power Surge

At the beginning of each player's upkeep, this enchantment deals X damage to that player, where X is the number of untapped lands they controlled at the beginning of this turn.

Mana Geyser

Add {R} for each tapped land your opponents control.

Pallimud

As this creature enters, choose an opponent.
Pallimud's power is equal to the number of tapped lands the chosen player controls.

Glissa Sunseeker

First strike
{T}: Destroy target artifact if its mana value is equal to the amount of unspent mana you have.

Ignition Team

This creature enters with X +1/+1 counters on it, where X is the number of tapped lands on the battlefield.
{2}{R}, Remove a +1/+1 counter from this creature: Target land becomes a 4/4 red Elemental creature until end of turn. It's still a land.

Horizon Stone

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

Pygmy Hippo

Whenever this creature attacks and isn't blocked, you may have defending player activate a mana ability of each land they control and lose all unspent mana. If you do, this creature assigns no combat damage this turn and at the beginning of your next main phase this turn, you add an amount of {C} equal to the amount of mana that player lost this way.

Kruphix, God of Horizons

Indestructible
As long as your devotion to green and blue is less than seven, Kruphix isn't a creature.
You have no maximum hand size.
If you would lose unspent mana, that mana becomes colorless instead.

Benthic Explorers

{T}, Untap a tapped land an opponent controls: Add one mana of any type that land could produce.

Manabarbs

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

Power Sink

Counter target spell unless its controller pays {X}. If that player doesn't, they tap all lands with mana abilities they control and lose all unspent mana.

Well of Discovery

At the beginning of your end step, if you control no untapped lands, draw a card.