Promising Vein

{T}: Add {C}.
{1}, {T}, Sacrifice Promising Vein: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Volatile Fault

{T}: Add {C}.
{1}, {T}, Sacrifice Volatile Fault: Destroy target nonbasic land an opponent controls. That player may search their library for a basic land card, put it onto the battlefield, then shuffle. You create a Treasure token.

Cavernous Maw

{T}: Add {C}.
{2}: Cavernous Maw becomes a 3/3 Elemental creature until end of turn. It's still a Cave land. Activate only if the number of other Caves you control plus the number of Cave cards in your graveyard is three or greater.

Hidden Courtyard

Hidden Courtyard enters tapped.
{T}: Add {W}.
{4}{W}, {T}, Sacrifice Hidden Courtyard: Discover 4. Activate only as a sorcery. (Exile cards from the top of your library until you exile a nonland card with mana value 4 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)

Hidden Necropolis

Hidden Necropolis enters tapped.
{T}: Add {B}.
{4}{B}, {T}, Sacrifice Hidden Necropolis: Discover 4. Activate only as a sorcery. (Exile cards from the top of your library until you exile a nonland card with mana value 4 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)

Sinuous Benthisaur

When Sinuous Benthisaur enters, look at the top X cards of your library, where X is the number of Caves you control plus the number of Cave cards in your graveyard. Put two of those cards into your hand and the rest on the bottom of your library in a random order.

Spelunking

When Spelunking enters, draw a card, then you may put a land card from your hand onto the battlefield. If you put a Cave onto the battlefield this way, you gain 4 life.
Lands you control enter untapped.

Kaslem's Strider

Kaslem's Stonetree

When Kaslem's Stonetree enters, look at the top six cards of your library. You may put a land card from among them onto the battlefield tapped. Put the rest on the bottom in a random order.
Craft with Cave {5}{G} ({5}{G}, Exile this artifact, Exile a Cave you control or a Cave card from your graveyard: Return this card transformed under its owner's control. Craft only as a sorcery.)

Kaslem's Stonetree // Kaslem's Strider

Mycoid Maze

(Transforms from Twists and Turns.)
{T}: Add {G}.
{3}{G}, {T}: Look at the top four cards of your library. You may reveal a creature card from among them and put that card into your hand. Put the rest on the bottom of your library in a random order.

Twists and Turns

If a creature you control would explore, instead you scry 1, then that creature explores.
When Twists and Turns enters, target creature you control explores.
When a land you control enters, if you control seven or more lands, transform Twists and Turns.

Twists and Turns // Mycoid Maze

Hidden Volcano

Hidden Volcano enters tapped.
{T}: Add {R}.
{4}{R}, {T}, Sacrifice Hidden Volcano: Discover 4. Activate only as a sorcery. (Exile cards from the top of your library until you exile a nonland card with mana value 4 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)

Echoing Deeps

You may have Echoing Deeps enter tapped as a copy of any land card in a graveyard, except it's a Cave in addition to its other types.
{T}: Add {C}.

Compass Gnome

When Compass Gnome enters, you may search your library for a basic land card or Cave card, reveal it, then shuffle and put that card on top.

Tecutlan, the Searing Rift

(Transforms from Brass's Tunnel-Grinder.)
{T}: Add {R}.
Whenever you cast a permanent spell using mana produced by Tecutlan, the Searing Rift, discover X, where X is that spell's mana value.

Brass's Tunnel-Grinder

When Brass's Tunnel-Grinder enters, discard any number of cards, then draw that many cards plus one.
At the beginning of your end step, if you descended this turn, put a bore counter on Brass's Tunnel-Grinder. Then if there are three or more bore counters on it, remove those counters and transform it. (You descended if a permanent card was put into your graveyard from anywhere.)

Brass's Tunnel-Grinder // Tecutlan, the Searing Rift

Cosmium Confluence

Choose three. You may choose the same mode more than once.
• Search your library for a Cave card, put it onto the battlefield tapped, then shuffle.
• Put three +1/+1 counters on a Cave you control. It becomes a 0/0 Elemental creature with haste. It's still a land.
• Destroy target enchantment.

Captivating Cave

{T}: Add {C}.
{1}, {T}: Add one mana of any color.
{4}, {T}, Sacrifice Captivating Cave: Put two +1/+1 counters on target creature. Activate only as a sorcery.

The Tomb of Aclazotz

(Transforms from Tarrian's Journal.)
{T}: Add {B}.
{T}: You may cast a creature spell from your graveyard this turn. If you do, it enters with a finality counter on it and is a Vampire in addition to its other types. (If a creature with a finality counter on it would die, exile it instead.)

Tarrian's Journal

{T}, Sacrifice another artifact or creature: Draw a card. Activate only as a sorcery.
{2}, {T}, Discard your hand: Transform Tarrian's Journal.

Tarrian's Journal // The Tomb of Aclazotz

Bat Colony

When Bat Colony enters, create a 1/1 black Bat creature token with flying for each mana from a Cave spent to cast it.
Whenever a Cave you control enters, put a +1/+1 counter on target creature you control.

Sunken Citadel

Sunken Citadel enters tapped. As it enters, choose a color.
{T}: Add one mana of the chosen color.
{T}: Add two mana of the chosen color. Spend this mana only to activate abilities of land sources.

Shadows' Lair

(Transforms from Grasping Shadows.)
{T}: Add {B}.
{B}, {T}, Remove a dread counter from Shadows' Lair: You draw a card and you lose 1 life.

Grasping Shadows

Whenever a creature you control attacks alone, it gains deathtouch and lifelink until end of turn. Put a dread counter on Grasping Shadows. Then if there are three or more dread counters on it, transform it.

Grasping Shadows // Shadows' Lair

Calamitous Cave-In

Calamitous Cave-In deals X damage to each creature and each planeswalker, where X is the number of Caves you control plus the number of Cave cards in your graveyard.

Forgotten Monument

{T}: Add {C}.
Other Caves you control have "{T}, Pay 1 life: Add one mana of any color."

Hidden Cataract

Hidden Cataract enters tapped.
{T}: Add {U}.
{4}{U}, {T}, Sacrifice Hidden Cataract: Discover 4. Activate only as a sorcery. (Exile cards from the top of your library until you exile a nonland card with mana value 4 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)

Gargantuan Leech

This spell costs {1} less to cast for each Cave you control and each Cave card in your graveyard.
Lifelink

Glimpse the Core

Choose one —
• Search your library for a basic Forest card, put that card onto the battlefield tapped, then shuffle.
• Return target Cave card from your graveyard to the battlefield tapped.

Pit of Offerings

Pit of Offerings enters tapped.
When Pit of Offerings enters, exile up to three target cards from graveyards.
{T}: Add {C}.
{T}: Add one mana of any of the exiled cards' colors.

Hidden Nursery

Hidden Nursery enters tapped.
{T}: Add {G}.
{4}{G}, {T}, Sacrifice Hidden Nursery: Discover 4. Activate only as a sorcery. (Exile cards from the top of your library until you exile a nonland card with mana value 4 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)