mtg.wtf

{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to pay Un-costs.

Underground Mortuary enters tapped.
When Underground Mortuary enters, surveil 1.

{T}: Add {C}.
{T}: Add {U} or {B}. Underground River deals 1 damage to you.

If damage would be dealt to Undergrowth Champion while it has a +1/+1 counter on it, prevent that damage and remove a +1/+1 counter from Undergrowth Champion.
Landfall — Whenever a land you control enters, put a +1/+1 counter on Undergrowth Champion.

At the beginning of your upkeep, return target land card from your graveyard to the battlefield tapped.

Undergrowth Scavenger enters with a number of +1/+1 counters on it equal to the number of creature cards in all graveyards.

Undergrowth Stadium enters tapped unless you have two or more opponents.
{T}: Add {B} or {G}.

Whenever an artifact you control enters, you may pay {1}. If you do, each opponent loses 1 life and you gain 1 life.
{1}{B}, Sacrifice Underhanded Designs: Destroy target creature. Activate only if you control two or more artifacts.

Counter target spell. Its controller loses 3 life.

Vigilance
When Undermountain Adventurer enters, you take the initiative.
{T}: Add {G}{G}. If you've completed a dungeon, add six {G} instead.

If you would draw a card, instead look at the top three cards of your library, then put one into your hand and the rest into your graveyard.
Pay 4 life: Underrealm Lich gains indestructible until end of turn. Tap it.

Flash
Undersea Invader enters tapped.

Choose target spell. If it's a creature spell, it perpetually gets -2/-0. Counter that spell unless its controller pays {2}.

When you unlock this door, surveil 2.

Each nonland card in your graveyard has escape. The escape cost is equal to the card's mana cost plus exile three other cards from your graveyard.
At the beginning of the end step, sacrifice Underworld Breach.

Underworld Charger can't block.
Escape — {4}{B}, Exile three other cards from your graveyard.
Underworld Charger escapes with two +1/+1 counters on it.

Constellation — Whenever Underworld Coinsmith or another enchantment you control enters, you gain 1 life.
{W}{B}, Pay 1 life: Each opponent loses 1 life.

Enchant land
Enchanted land has "{T}, Pay 1 life: Draw a card."

Whenever an opponent draws a card, Underworld Dreams deals 1 damage to that player.

Underworld Fires deals 1 damage to each creature and each planeswalker. If a permanent dealt damage this way would die this turn, exile it instead.

When Underworld Hermit enters, create a number of 1/1 green Squirrel creature tokens equal to your devotion to black.

Underworld Rage-Hound attacks each combat if able.
Escape — {3}{R}, Exile three other cards from your graveyard.
Underworld Rage-Hound escapes with a +1/+1 counter on it.

Whenever Underworld Sentinel attacks, exile target creature card from your graveyard.
When Underworld Sentinel dies, put all cards exiled with it onto the battlefield.

{T}: Add one mana of any color. During your next untap step, as you untap your permanents, return Undiscovered Paradise to its owner's hand.