Sefris of the Hidden Ways

Whenever one or more creature cards are put into your graveyard from anywhere, venture into the dungeon. This ability triggers only once each turn. (To venture into the dungeon, enter the first room or advance to the next room.)
Create Undead — Whenever you complete a dungeon, return target creature card from your graveyard to the battlefield.

Radiant Solar

Flying, lifelink
Whenever this creature or another nontoken creature you control enters, venture into the dungeon. (Enter the first room or advance to the next room.)
{W}, Discard this card: Venture into the dungeon and you gain 3 life.

Verdant Catacombs

{T}, Pay 1 life, Sacrifice this land: Search your library for a Swamp or Forest card, put it onto the battlefield, then shuffle.

Arid Mesa

{T}, Pay 1 life, Sacrifice this land: Search your library for a Mountain or Plains card, put it onto the battlefield, then shuffle.

Sea of Clouds

This land enters tapped unless you have two or more opponents.
{T}: Add {W} or {U}.

Triumphant Adventurer

Deathtouch
During your turn, this creature has first strike.
Whenever this creature attacks, venture into the dungeon. (Enter the first room or advance to the next room.)

Bar the Gate

Counter target creature or planeswalker spell. Venture into the dungeon. (Enter the first room or advance to the next room.)

Seasoned Dungeoneer

When this creature enters, you take the initiative.
Whenever you attack, target attacking Cleric, Rogue, Warrior, or Wizard gains protection from creatures until end of turn. It explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on the creature, then put the card back or put it into your graveyard.)

Wooded Foothills

{T}, Pay 1 life, Sacrifice this land: Search your library for a Mountain or Forest card, put it onto the battlefield, then shuffle.

White Plume Adventurer

When this creature enters, you take the initiative.
At the beginning of each opponent's upkeep, untap a creature you control. If you've completed a dungeon, untap all creatures you control instead.

Shattered Sanctum

This land enters tapped unless you control two or more other lands.
{T}: Add {W} or {B}.

Vault of Champions

This land enters tapped unless you have two or more opponents.
{T}: Add {W} or {B}.

Underground River

{T}: Add {C}.
{T}: Add {U} or {B}. This land deals 1 damage to you.

Midnight Pathlighter

Creatures you control can't be blocked except by legendary creatures.
Whenever one or more creatures you control deal combat damage to a player, venture into the dungeon. (Enter the first room or advance to the next room.)

Adarkar Wastes

{T}: Add {C}.
{T}: Add {W} or {U}. This land deals 1 damage to you.

Acererak the Archlich

When Acererak enters, if you haven't completed Tomb of Annihilation, return Acererak to its owner's hand and venture into the dungeon.
Whenever Acererak attacks, for each opponent, you create a 2/2 black Zombie creature token unless that player sacrifices a creature of their choice.

Thorough Investigation

Whenever you attack, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.")
Whenever you sacrifice a Clue, venture into the dungeon. (Enter the first room or advance to the next room.)

Dungeon Map

{T}: Add {C}.
{3}, {T}: Venture into the dungeon. Activate only as a sorcery. (Enter the first room or advance to the next room.)

Ravenloft Adventurer

When this creature enters, you take the initiative.
If a creature an opponent controls would die, instead exile it and put a hit counter on it.
Whenever this creature attacks, if you've completed a dungeon, defending player loses 1 life for each card they own in exile with a hit counter on it.

Swamp

Hallowed Fountain

({T}: Add {W} or {U}.)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Glacial Fortress

This land enters tapped unless you control a Plains or an Island.
{T}: Add {W} or {U}.

Drowned Catacomb

This land enters tapped unless you control an Island or a Swamp.
{T}: Add {U} or {B}.

Enchant creature
Enchanted creature has flying and "Whenever this creature deals combat damage to a player, venture into the dungeon." (Enter the first room or advance to the next room.)

Deserted Beach

This land enters tapped unless you control two or more other lands.
{T}: Add {W} or {U}.

Tomb of Horrors Adventurer

When this creature enters, you take the initiative.
Whenever you cast your second spell each turn, copy it. If you've completed a dungeon, copy that spell twice instead. You may choose new targets for the copies. (A copy of a permanent spell becomes a token.)

Dungeoneer's Pack

This artifact enters tapped.
{2}, {T}, Sacrifice this artifact: You take the initiative, gain 3 life, draw a card, and create a Treasure token. Activate only as a sorcery. (A Treasure token is an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

From the Catacombs

Put target creature card from a graveyard onto the battlefield under your control with a corpse counter on it. You take the initiative. If that creature would leave the battlefield, exile it instead of putting it anywhere else.
Escape—{3}{B}{B}, Exile five other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)

Yuan-Ti Malison

This creature can't be blocked as long as it's attacking alone.
Whenever this creature deals combat damage to a player, venture into the dungeon. (Enter the first room or advance to the next room.)

Misty Rainforest

{T}, Pay 1 life, Sacrifice this land: Search your library for a Forest or Island card, put it onto the battlefield, then shuffle.

Marsh Flats

{T}, Pay 1 life, Sacrifice this land: Search your library for a Plains or Swamp card, put it onto the battlefield, then shuffle.

Flooded Strand

{T}, Pay 1 life, Sacrifice this land: Search your library for a Plains or Island card, put it onto the battlefield, then shuffle.

Morphic Pool

This land enters tapped unless you have two or more opponents.
{T}: Add {U} or {B}.

Nadaar, Selfless Paladin

Vigilance
Whenever Nadaar enters or attacks, venture into the dungeon. (Enter the first room or advance to the next room.)
Other creatures you control get +1/+1 as long as you've completed a dungeon.

Safana, Calimport Cutthroat

Menace
At the beginning of your end step, if you have the initiative, create a Treasure token. Create three of those tokens instead if you've completed a dungeon.
Choose a Background (You can have a Background as a second commander.)

Plains

Raffine's Tower

({T}: Add {W}, {U}, or {B}.)
This land enters tapped.
Cycling {3} ({3}, Discard this card: Draw a card.)

Island

Godless Shrine

({T}: Add {W} or {B}.)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Displacer Beast

When this creature enters, venture into the dungeon. (Enter the first room or advance to the next room.)
Displacement — {3}{U}: Return this creature to its owner's hand.

Caves of Koilos

{T}: Add {C}.
{T}: Add {W} or {B}. This land deals 1 damage to you.

Windswept Heath

{T}, Pay 1 life, Sacrifice this land: Search your library for a Forest or Plains card, put it onto the battlefield, then shuffle.

City of Brass

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

Sunken Hollow

({T}: Add {U} or {B}.)
This land enters tapped unless you control two or more basic lands.

Prairie Stream

({T}: Add {W} or {U}.)
This land enters tapped unless you control two or more basic lands.

Shipwreck Marsh

This land enters tapped unless you control two or more other lands.
{T}: Add {U} or {B}.

Immovable Rod

You may choose not to untap this artifact during your untap step.
Whenever this artifact becomes untapped, venture into the dungeon.
{3}{W}, {T}: For as long as this artifact remains tapped, another target permanent loses all abilities and can't attack or block.

Isolated Chapel

This land enters tapped unless you control a Plains or a Swamp.
{T}: Add {W} or {B}.

Dungeon Descent

This land enters tapped.
{T}: Add {C}.
{4}, {T}, Tap an untapped legendary creature you control: Venture into the dungeon. Activate only as a sorcery. (Enter the first room or advance to the next room.)

Polluted Delta

{T}, Pay 1 life, Sacrifice this land: Search your library for an Island or Swamp card, put it onto the battlefield, then shuffle.

Mana Confluence

{T}, Pay 1 life: Add one mana of any color.

Barrowin of Clan Undurr

When Barrowin enters, venture into the dungeon. (Enter the first room or advance to the next room.)
Whenever Barrowin attacks, return up to one creature card with mana value 3 or less from your graveyard to the battlefield if you've completed a dungeon.

Bloodstained Mire

{T}, Pay 1 life, Sacrifice this land: Search your library for a Swamp or Mountain card, put it onto the battlefield, then shuffle.

Sarevok's Tome

When this artifact enters, you take the initiative.
{T}: Add {C}. If you have the initiative, add {C}{C} instead.
{3}, {T}: Exile cards from the top of your library until you exile a nonland card. You may cast that card without paying its mana cost. Activate only if you've completed a dungeon.

Watery Grave

({T}: Add {U} or {B}.)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Displacer Kitten

Avoidance — Whenever you cast a noncreature spell, exile up to one target nonland permanent you control, then return that card to the battlefield under its owner's control.

Scalding Tarn

{T}, Pay 1 life, Sacrifice this land: Search your library for an Island or Mountain card, put it onto the battlefield, then shuffle.