Opposition Agent

Flash
You control your opponents while they're searching their libraries.
While an opponent is searching their library, they exile each card they find. You may play those cards for as long as they remain exiled, and you may spend mana as though it were mana of any color to cast them.

Oblivion Crown

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature
Enchanted creature has "Discard a card: This creature gets +1/+1 until end of turn."

Culling the Weak

As an additional cost to cast this spell, sacrifice a creature.
Add {B}{B}{B}{B}.

Putrid Imp

Discard a card: Putrid Imp gains flying until end of turn.
Threshold — As long as seven or more cards are in your graveyard, Putrid Imp gets +1/+1 and can't block.

Boreal Druid

Command Beacon

{T}: Add {C}.
{T}, Sacrifice Command Beacon: Put your commander into your hand from the command zone.

Deathrite Shaman

{T}: Exile target land card from a graveyard. Add one mana of any color.
{B}, {T}: Exile target instant or sorcery card from a graveyard. Each opponent loses 2 life.
{G}, {T}: Exile target creature card from a graveyard. You gain 2 life.

Undergrowth Stadium

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

Nurturing Peatland

{T}, Pay 1 life: Add {B} or {G}.
{1}, {T}, Sacrifice Nurturing Peatland: Draw a card.

Golgari Grave-Troll

Golgari Grave-Troll enters with a +1/+1 counter on it for each creature card in your graveyard.
{1}, Remove a +1/+1 counter from Golgari Grave-Troll: Regenerate Golgari Grave-Troll.
Dredge 6 (If you would draw a card, you may mill six cards instead. If you do, return this card from your graveyard to your hand.)

Dark Ritual

Forbidden Orchard

{T}: Add one mana of any color.
Whenever you tap Forbidden Orchard for mana, target opponent creates a 1/1 colorless Spirit creature token.

Ramunap Excavator

City of Brass

Whenever City of Brass becomes tapped, it deals 1 damage to you.
{T}: Add one mana of any color.

Rain of Filth

Until end of turn, lands you control gain "Sacrifice this land: Add {B}."

Llanowar Elves

Command Tower

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

Life from the Loam

Return up to three target land cards from your graveyard to your hand.
Dredge 3 (If you would draw a card, you may mill three cards instead. If you do, return this card from your graveyard to your hand.)

Crop Rotation

As an additional cost to cast this spell, sacrifice a land.
Search your library for a land card, put that card onto the battlefield, then shuffle.

Elvish Spirit Guide

Exile Elvish Spirit Guide from your hand: Add {G}.

Joraga Treespeaker

Level up {1}{G} ({1}{G}: Put a level counter on this. Level up only as a sorcery.)
LEVEL 1-4
1/2
{T}: Add {G}{G}.
LEVEL 5+
1/4
Elves you control have "{T}: Add {G}{G}."

Collector Ouphe

Activated abilities of artifacts can't be activated.

Assassin's Trophy

Destroy target permanent an opponent controls. Its controller may search their library for a basic land card, put it onto the battlefield, then shuffle.

The Gitrog Monster

Deathtouch
At the beginning of your upkeep, sacrifice The Gitrog Monster unless you sacrifice a land.
You may play an additional land on each of your turns.
Whenever one or more land cards are put into your graveyard from anywhere, draw a card.

Plunge into Darkness

Choose one —
• Sacrifice any number of creatures. You gain 3 life for each creature sacrificed this way.
• Pay any amount of life, then look at that many cards from the top of your library. Put one of those cards into your hand and exile the rest.
Entwine {B} (Choose both if you pay the entwine cost.)

Forest

Sol Ring

Llanowar Wastes

{T}: Add {C}.
{T}: Add {B} or {G}. Llanowar Wastes deals 1 damage to you.

Dakmor Salvage

Dakmor Salvage enters tapped.
{T}: Add {B}.
Dredge 2 (If you would draw a card, you may mill two cards instead. If you do, return this card from your graveyard to your hand.)

Snow-Covered Swamp

Elvish Mystic

Sylvan Safekeeper

Sacrifice a land: Target creature you control gains shroud until end of turn. (It can't be the target of spells or abilities.)

Grim Tutor

Search your library for a card, put that card into your hand, then shuffle. You lose 3 life.

Cabal Ritual

Add {B}{B}{B}.
Threshold — Add {B}{B}{B}{B}{B} instead if seven or more cards are in your graveyard.

Noose Constrictor

Reach
Discard a card: Noose Constrictor gets +1/+1 until end of turn.

Fyndhorn Elves

Chord of Calling

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Search your library for a creature card with mana value X or less, put it onto the battlefield, then shuffle.

Squandered Resources

Sacrifice a land: Add one mana of any type the sacrificed land could produce.

Tainted Pact

Exile the top card of your library. You may put that card into your hand unless it has the same name as another card exiled this way. Repeat this process until you put a card into your hand or you exile two cards with the same name, whichever comes first.

Wild Growth

Enchant land
Whenever enchanted land is tapped for mana, its controller adds an additional {G}.

Twilight Mire

{T}: Add {C}.
{B/G}, {T}: Add {B}{B}, {B}{G}, or {G}{G}.

Eldritch Evolution

As an additional cost to cast this spell, sacrifice a creature.
Search your library for a creature card with mana value X or less, where X is 2 plus the sacrificed creature's mana value. Put that card onto the battlefield, then shuffle. Exile Eldritch Evolution.

Dauthi Voidwalker

Shadow (This creature can block or be blocked by only creatures with shadow.)
If a card would be put into an opponent's graveyard from anywhere, instead exile it with a void counter on it.
{T}, Sacrifice Dauthi Voidwalker: Choose an exiled card an opponent owns with a void counter on it. You may play it this turn without paying its mana cost.

Veil of Summer

Draw a card if an opponent has cast a blue or black spell this turn. Spells you control can't be countered this turn. You and permanents you control gain hexproof from blue and from black until end of turn. (You and they can't be the targets of blue or black spells or abilities your opponents control.)

Green Sun's Zenith

Search your library for a green creature card with mana value X or less, put it onto the battlefield, then shuffle. Shuffle Green Sun's Zenith into its owner's library.

Swamp

Ulcerate

Target creature gets -3/-3 until end of turn. You lose 3 life.

Priest of Titania

{T}: Add {G} for each Elf on the battlefield.

Autumn's Veil

Spells you control can't be countered by blue or black spells this turn, and creatures you control can't be the targets of blue or black spells this turn.

Abrupt Decay

This spell can't be countered.
Destroy target nonland permanent with mana value 3 or less.

Snow-Covered Forest

Birds of Paradise

Elves of Deep Shadow

{T}: Add {B}. Elves of Deep Shadow deals 1 damage to you.

Grist, the Hunger Tide

As long as Grist, the Hunger Tide isn't on the battlefield, it's a 1/1 Insect creature in addition to its other types.
+1: Create a 1/1 black and green Insect creature token, then mill a card. If an Insect card was milled this way, put a loyalty counter on Grist and repeat this process.
−2: You may sacrifice a creature. When you do, destroy target creature or planeswalker.
−5: Each opponent loses life equal to the number of creature cards in your graveyard.

Ad Nauseam

Reveal the top card of your library and put that card into your hand. You lose life equal to its mana value. You may repeat this process any number of times.

Summoner's Pact

Search your library for a green creature card, reveal it, put it into your hand, then shuffle.
At the beginning of your next upkeep, pay {2}{G}{G}. If you don't, you lose the game.