Explore the Underdark

Search your library for up to two basic land cards and/or Gate cards, put them onto the battlefield tapped, then shuffle.
You take the initiative.

Scale Deflection

Put two +1/+1 counters on target creature and untap it. It gains hexproof until end of turn. (Then exile this card. You may cast the creature later from exile.)

Dread Linnorm

This creature can't be blocked by creatures with power 3 or less.

Dread Linnorm // Scale Deflection

Terror of the Peaks

Flying
Spells your opponents cast that target this creature cost an additional 3 life to cast.
Whenever another creature you control enters, this creature deals damage equal to that creature's power to any target.

Marble Diamond

This artifact enters tapped.
{T}: Add {W}.

Noxious Dragon

Flying
When this creature dies, you may destroy target creature with mana value 3 or less.

Wind-Scarred Crag

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {R} or {W}.

Black Dragon

Flying
Acid Breath — When this creature enters, target creature an opponent controls gets -3/-3 until end of turn.

Greatsword of Tyr

Whenever equipped creature attacks, put a +1/+1 counter on it and tap up to one target creature defending player controls.
Equip {W} ({W}: Attach to target creature you control. Equip only as a sorcery.)

Power Word Kill

Destroy target non-Angel, non-Demon, non-Devil, non-Dragon creature.

Frontier Bivouac

This land enters tapped.
{T}: Add {G}, {U}, or {R}.

O-Kagachi, Vengeful Kami

Flying, trample
Whenever O-Kagachi deals combat damage to a player, if that player attacked you during their last turn, exile target nonland permanent that player controls.

Rimewood Falls

({T}: Add {G} or {U}.)
This land enters tapped.

Heap Gate

{T}: Add {C}.
{1}, {T}: Add one mana of any color.
{1}, {T}, Tap an untapped Gate you control: Create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Lurking Green Dragon

Flying
This creature can't attack unless defending player controls a creature with flying.

Primevals' Glorious Rebirth

(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Return all legendary permanent cards from your graveyard to the battlefield.

Majestic Genesis

Reveal the top X cards of your library, where X is the greatest mana value of a commander you own on the battlefield or in the command zone. You may put any number of permanent cards from among them onto the battlefield. Put the rest on the bottom of your library in a random order.

Urza's Ruinous Blast

(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Exile all nonland permanents that aren't legendary.

Jade Orb of Dragonkind

{T}: Add {G}. When you spend this mana to cast a Dragon creature spell, it enters with an additional +1/+1 counter on it and gains hexproof until your next turn. (It can't be the target of spells or abilities your opponents control.)

Patron of the Arts

When this creature enters or dies, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Izzet Guildgate

This land enters tapped.
{T}: Add {U} or {R}.

Summon Undead

You may mill three cards. Then return a creature card from your graveyard to the battlefield. (To mill a card, put the top card of your library into your graveyard.)

Lozhan, Dragons' Legacy

Flying
Whenever you cast an Adventure or Dragon spell, Lozhan deals damage equal to that spell's mana value to any target that isn't a commander.

Maelstrom Archangel

Flying
Whenever this creature deals combat damage to a player, you may cast a spell from your hand without paying its mana cost.

Red Dragon

Flying
Fire Breath — When this creature enters, it deals 4 damage to each opponent.

Rakdos Guildgate

This land enters tapped.
{T}: Add {B} or {R}.

Jungle Shrine

This land enters tapped.
{T}: Add {R}, {G}, or {W}.

Reaper's Talisman

Whenever equipped creature attacks, it gains deathtouch until end of turn.
Whenever equipped creature attacks alone, defending player loses 2 life and you gain 2 life.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Golgari Guildgate

This land enters tapped.
{T}: Add {B} or {G}.

Nomad Outpost

This land enters tapped.
{T}: Add {R}, {W}, or {B}.

Fire Diamond

This artifact enters tapped.
{T}: Add {R}.

Miirym, Sentinel Wyrm

Flying, ward {2}
Whenever another nontoken Dragon you control enters, create a token that's a copy of it, except the token isn't legendary.

Zoological Study

Mill five cards, then return a creature card milled this way to your hand. (Then exile this card. You may cast the artifact later from exile.)

Monster Manual

{1}{G}, {T}: You may put a creature card from your hand onto the battlefield.

Monster Manual // Zoological Study

Akoum Refuge

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {B} or {R}.

Ancient Silver Dragon

Flying
Whenever this creature deals combat damage to a player, roll a d20. Draw cards equal to the result. You have no maximum hand size for the rest of the game.

Simic Guildgate

This land enters tapped.
{T}: Add {G} or {U}.

Draconic Muralists

When this creature dies, you may search your library for a Dragon card, reveal it, put it into your hand, then shuffle.

Charcoal Diamond

This artifact enters tapped.
{T}: Add {B}.

Nature's Lore

Search your library for a Forest card, put that card onto the battlefield, then shuffle.

Timeless Lotus

Timeless Lotus enters tapped.
{T}: Add {W}{U}{B}{R}{G}.

Jaded Sell-Sword

When this creature enters, if mana from a Treasure was spent to cast it, it gains first strike and haste until end of turn.

Skanos Dragonheart

Whenever Skanos Dragonheart attacks, it gets +X/+X until end of turn, where X is the greatest power among other Dragons you control and Dragon cards in your graveyard.
Choose a Background (You can have a Background as a second commander.)

Gateway Plaza

This land enters tapped.
When this land enters, sacrifice it unless you pay {1}.
{T}: Add one mana of any color.

Citadel Gate

This land enters tapped.
As this land enters, choose a color other than white.
{T}: Add {W} or one mana of the chosen color.

Icingdeath, Frost Tyrant

Flying, vigilance
When Icingdeath, Frost Tyrant dies, create Icingdeath, Frost Tongue, a legendary white Equipment artifact token with "Equipped creature gets +2/+0," "Whenever equipped creature attacks, tap target creature defending player controls," and equip {2}.

Manor Gate

This land enters tapped.
As this land enters, choose a color other than green.
{T}: Add {G} or one mana of the chosen color.

Ambitious Dragonborn

This creature enters with X +1/+1 counters on it, where X is the greatest power among creatures you control and creature cards in your graveyard.

Cliffgate

This land enters tapped.
As this land enters, choose a color other than red.
{T}: Add {R} or one mana of the chosen color.

Glacial Floodplain

({T}: Add {W} or {U}.)
This land enters tapped.

Livaan, Cultist of Tiamat

Whenever you cast a noncreature spell, target creature gets +X/+0 until end of turn, where X is that spell's mana value.
Choose a Background (You can have a Background as a second commander.)

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Bathe in Gold

Create a Treasure token. (Then exile this card. You may cast the creature later from exile.)

Young Red Dragon

Young Red Dragon // Bathe in Gold

Simic Signet

Moss Diamond

This artifact enters tapped.
{T}: Add {G}.

Mystic Monastery

This land enters tapped.
{T}: Add {U}, {R}, or {W}.

Forktail Sweep

Forktail Sweep deals 1 damage to each creature you don't control. (Then exile this card. You may cast the creature later from exile.)

Fang Dragon

Fang Dragon // Forktail Sweep

Ancient Copper Dragon

Flying
Whenever this creature deals combat damage to a player, roll a d20. You create a number of Treasure tokens equal to the result.

Baldur's Gate

{T}: Add {C}.
{2}, {T}: Add X mana of any one color, where X is the number of other Gates you control.

Crucible of Fire

Dragon's Fire

As an additional cost to cast this spell, you may reveal a Dragon card from your hand or choose a Dragon you control.
Dragon's Fire deals 3 damage to target creature or planeswalker. If you revealed a Dragon card or chose a Dragon as you cast this spell, Dragon's Fire deals damage equal to the power of that card or creature instead.

Woodland Chasm

({T}: Add {B} or {G}.)
This land enters tapped.

Adult Gold Dragon

Entropic Cloud

Creatures you control gain deathtouch until end of turn. (Then exile this card. You may cast the creature later from exile.)

Topaz Dragon

Topaz Dragon // Entropic Cloud

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.

Darigaaz Reincarnated

Flying, trample, haste
If Darigaaz would die, instead exile it with three egg counters on it.
At the beginning of your upkeep, if this card is exiled with an egg counter on it, remove an egg counter from it. Then if this card has no egg counters on it, return it to the battlefield.

Jodah, the Unifier

Legendary creatures you control get +X/+X, where X is the number of legendary creatures you control.
Whenever you cast a legendary spell from your hand, exile cards from the top of your library until you exile a legendary nonland card with lesser mana value. You may cast that card without paying its mana cost. Put the rest on the bottom of your library in a random order.

Simic Growth Chamber

This land enters tapped.
When this land enters, return a land you control to its owner's hand.
{T}: Add {G}{U}.

Earthquake Dragon

This spell costs {X} less to cast, where X is the total mana value of Dragons you control.
Flying, trample
{2}{G}, Sacrifice a land: Return this card from your graveyard to your hand.

Dimir Guildgate

This land enters tapped.
{T}: Add {U} or {B}.

Seaside Citadel

This land enters tapped.
{T}: Add {G}, {W}, or {U}.

Bladewing, Deathless Tyrant

Flying, haste
Whenever Bladewing deals combat damage to a player or planeswalker, for each creature card in your graveyard, create a 2/2 black Zombie Knight creature token with menace.

Extinction

Destroy all creatures of the creature type of your choice.

Dragon Arch

{2}, {T}: You may put a multicolored creature card from your hand onto the battlefield.

Opulent Palace

This land enters tapped.
{T}: Add {B}, {G}, or {U}.

Gruul Signet

Savage Lands

This land enters tapped.
{T}: Add {B}, {R}, or {G}.

Acolyte of Bahamut

Commander creatures you own have "The first Dragon spell you cast each turn costs {2} less to cast."

Basilisk Gate

{T}: Add {C}.
{2}, {T}: Target creature gets +X/+X until end of turn, where X is the number of Gates you control. Activate only as a sorcery.

Alpine Meadow

({T}: Add {R} or {W}.)
This land enters tapped.

Korlessa, Scale Singer

You may look at the top card of your library any time.
You may cast Dragon spells from the top of your library.

Sandsteppe Citadel

This land enters tapped.
{T}: Add {W}, {B}, or {G}.

Thornwood Falls

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {G} or {U}.

Avenging Hunter

Trample
When this creature enters, you take the initiative.

Ganax, Astral Hunter

Flying
Whenever Ganax or another Dragon you control enters, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")
Choose a Background (You can have a Background as a second commander.)

Murder

Black Dragon Gate

This land enters tapped.
As this land enters, choose a color other than black.
{T}: Add {B} or one mana of the chosen color.

Atarka, World Render

Flying, trample
Whenever a Dragon you control attacks, it gains double strike until end of turn.

Instrument of the Bards

At the beginning of your upkeep, you may put a harmony counter on Instrument of the Bards.
{3}{G}, {T}: Search your library for a creature card with mana value equal to the number of harmony counters on Instrument of the Bards, reveal it, and put it into your hand. If that card is legendary, create a Treasure token. Then shuffle.

Blue Dragon

Flying
Lightning Breath — When this creature enters, until your next turn, target creature an opponent controls gets -3/-0, up to one other target creature gets -2/-0, and up to one other target creature gets -1/-0.

Renari, Merchant of Marvels

You may cast Dragon spells and artifact spells as though they had flash.
Choose a Background (You can have a Background as a second commander.)

Boros Guildgate

This land enters tapped.
{T}: Add {R} or {W}.

Merciless Eviction

Choose one —
• Exile all artifacts.
• Exile all creatures.
• Exile all enchantments.
• Exile all planeswalkers.

Ragefire Hellkite

Flying
Whenever this creature attacks, you may sacrifice another creature. If you do, this creature gains double strike until end of turn.

Breath Weapon

Breath Weapon deals 2 damage to each non-Dragon creature.

Sky Diamond

This artifact enters tapped.
{T}: Add {U}.

Two-Headed Hellkite

Flying, menace, haste
Whenever this creature attacks, draw two cards.

Arcane Sanctum

This land enters tapped.
{T}: Add {W}, {U}, or {B}.

Azorius Guildgate

This land enters tapped.
{T}: Add {W} or {U}.