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.

Woodland Wanderer

Vigilance, trample
Converge — Woodland Wanderer enters with a +1/+1 counter on it for each color of mana spent to cast it.

Swamp

Izzet Guildgate

Izzet Guildgate enters tapped.
{T}: Add {U} or {R}.

Reckless Handling

Search your library for an artifact card, reveal it, put it into your hand, shuffle, then discard a card at random. If an artifact card was discarded this way, Reckless Handling deals 2 damage to each opponent.

Snow-Covered Island

Arcane Signet

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

Orzhov Guildgate

Orzhov Guildgate enters tapped.
{T}: Add {W} or {B}.

The Fair Basilica

The Fair Basilica enters tapped.
{T}: Add {W}.
{1}{W}, {T}, Sacrifice The Fair Basilica: Draw a card.

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.

Saruli Gatekeepers

When Saruli Gatekeepers enters, if you control two or more Gates, you gain 7 life.

Glimmerpost

When Glimmerpost enters, you gain 1 life for each Locus on the battlefield.
{T}: Add {C}.

Doorkeeper

Defender
{2}{U}, {T}: Target player mills X cards, where X is the number of creatures you control with defender.

Door to Nothingness

Door to Nothingness enters tapped.
{W}{W}{U}{U}{B}{B}{R}{R}{G}{G}, {T}, Sacrifice Door to Nothingness: Target player loses the game.

Crackling Perimeter

Tap an untapped Gate you control: Crackling Perimeter deals 1 damage to each opponent.

Kick in the Door

Put a +1/+1 counter on target creature. That creature gains haste until end of turn and can't be blocked by Walls this turn. Venture into the dungeon. (Enter the first room or advance to the next room.)

Oswald Fiddlebender

Magical Tinkering — {W}, {T}, Sacrifice an artifact: Search your library for an artifact card with mana value equal to 1 plus the sacrificed artifact's mana value, put it onto the battlefield, then shuffle. Activate only as a sorcery.

Gates Ablaze

Gates Ablaze deals X damage to each creature, where X is the number of Gates you control.

Snow-Covered Swamp

Maulfist Doorbuster

When Maulfist Doorbuster enters, you get {E}{E} (two energy counters).
Whenever Maulfist Doorbuster attacks, you may pay {E}. If you do, target creature can't block this turn.

Mountain

Pull from Eternity

Put target face-up exiled card into its owner's graveyard.

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 artifact: Add one mana of any color.")

Lux Artillery

Whenever you cast an artifact creature spell, it gains sunburst. (It enters with a +1/+1 counter on it for each color of mana spent to cast it.)
At the beginning of your end step, if there are thirty or more counters among artifacts and creatures you control, Lux Artillery deals 10 damage to each opponent.

Boros Guildgate

Boros Guildgate enters tapped.
{T}: Add {R} or {W}.

Bar the Door

Creatures you control get +0/+4 until end of turn.

The Dross Pits

The Dross Pits enters tapped.
{T}: Add {B}.
{1}{B}, {T}, Sacrifice The Dross Pits: Draw a card.

Ramos, Dragon Engine

Flying
Whenever you cast a spell, put a +1/+1 counter on Ramos, Dragon Engine for each of that spell's colors.
Remove five +1/+1 counters from Ramos: Add {W}{W}{U}{U}{B}{B}{R}{R}{G}{G}. Activate only once each turn.

Monument to Perfection

{3}, {T}: Search your library for a basic, Sphere, or Locus land card, reveal it, put it into your hand, then shuffle.
{3}: Monument to Perfection becomes a 9/9 Phyrexian Construct artifact creature, loses all abilities, and gains indestructible and toxic 9. Activate only if there are nine or more lands with different names among the basic, Sphere, and Locus lands you control.

Gate Colossus

This spell costs {1} less to cast for each Gate you control.
Gate Colossus can't be blocked by creatures with power 2 or less.
Whenever a Gate you control enters, you may put Gate Colossus from your graveyard on top of your library.

Gatecreeper Vine

Defender
When Gatecreeper Vine enters, you may search your library for a basic land card or a Gate card, reveal it, put it into your hand, then shuffle.

Dimir Guildgate

Dimir Guildgate enters tapped.
{T}: Add {U} or {B}.

Plains

Greenside Watcher

Gateway Plaza

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

Gruul Guildgate

Gruul Guildgate enters tapped.
{T}: Add {R} or {G}.

Snow-Covered Mountain

Guardian of the Great Door

As an additional cost to cast this spell, tap four untapped artifacts, creatures, and/or lands you control.
Flying

Thran Portal

Thran Portal enters tapped unless you control two or fewer other lands.
As Thran Portal enters, choose a basic land type.
Thran Portal is the chosen type in addition to its other types.
Mana abilities of Thran Portal cost an additional 1 life to activate.

Ogre Jailbreaker

Defender
Ogre Jailbreaker can attack as though it didn't have defender as long as you control a Gate.

Cliffgate

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

Snow-Covered Forest

Golgari Guildgate

Golgari Guildgate enters tapped.
{T}: Add {B} or {G}.

Skyship Weatherlight

When Skyship Weatherlight enters, search your library for any number of artifact and/or creature cards, exile them, then shuffle.
{4}, {T}: Choose a card at random that was exiled with Skyship Weatherlight. Put that card into its owner's hand.

Evolving Door

{1}, {T}, Sacrifice a creature: Count the colors of the sacrificed creature, then search your library for a creature card that's exactly that many colors plus one. Exile that card, then shuffle. You may cast the exiled card. Activate only as a sorcery.

Archway Angel

Flying
When Archway Angel enters, you gain 2 life for each Gate you control.

Simic Guildgate

Simic Guildgate enters tapped.
{T}: Add {G} or {U}.

Opaline Bracers

Sunburst (This enters with a charge counter on it for each color of mana spent to cast it.)
Equipped creature gets +X/+X, where X is the number of charge counters on Opaline Bracers.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Black Dragon Gate

Black Dragon Gate enters tapped.
As Black Dragon Gate enters, choose a color other than black.
{T}: Add {B} or one mana of the chosen color.

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.

Fallaji Wayfarer

Fallaji Wayfarer is all colors. This ability doesn't affect its color identity. (It can be in any deck whose commander's color identity includes green.)
Multicolored spells you cast have convoke. (Your creatures can help cast those spells. Each creature you tap while casting a multicolored spell pays for {1} or one mana of a color that creature is.)

Chamber Sentry

Chamber Sentry enters with a +1/+1 counter on it for each color of mana spent to cast it.
{X}, {T}, Remove X +1/+1 counters from Chamber Sentry: It deals X damage to any target.
{W}{U}{B}{R}{G}: Return Chamber Sentry from your graveyard to your hand.

Cloudpost

Cloudpost enters tapped.
{T}: Add {C} for each Locus on the battlefield.

Citadel Gate

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

All Suns' Dawn

For each color, return up to one target card of that color from your graveyard to your hand. Exile All Suns' Dawn.

Rakdos Guildgate

Rakdos Guildgate enters tapped.
{T}: Add {B} or {R}.

Island

Secret Door

Defender
{4}{U}: Venture into the dungeon. Activate only as a sorcery. (Enter the first room or advance to the next room.)

Plaza of Harmony

When Plaza of Harmony enters, if you control two or more Gates, you gain 3 life.
{T}: Add {C}.
{T}: Add one mana of any type that a Gate you control could produce.

The Autonomous Furnace

The Autonomous Furnace enters tapped.
{T}: Add {R}.
{1}{R}, {T}, Sacrifice The Autonomous Furnace: Draw a card.

Forest

Azorius Guildgate

Azorius Guildgate enters tapped.
{T}: Add {W} or {U}.

Cellar Door

{3}, {T}: Target player puts the bottom card of their library into their graveyard. If it's a creature card, you create a 2/2 black Zombie creature token.

Garrison Sergeant

Garrison Sergeant has double strike as long as you control a Gate.

Glaive of the Guildpact

Equipped creature gets +1/+0 for each Gate you control and has vigilance and menace. (A creature with menace can't be blocked except by two or more creatures.)
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

Transguild Courier

District Guide

When District Guide enters, you may search your library for a basic land card or Gate card, reveal it, put it into your hand, then shuffle.

Treasure Chest

{4}, Sacrifice Treasure Chest: Roll a d20.
1 | Trapped! — You lose 3 life.
2—9 | Create five Treasure tokens.
10—19 | You gain 3 life and draw three cards.
20 | Search your library for a card. If it's an artifact card, you may put it onto the battlefield. Otherwise, put that card into your hand. Then shuffle.

Gatekeeper Gargoyle

Flying
Gatekeeper Gargoyle enters with a +1/+1 counter on it for each Gate you control.

Vexing Puzzlebox

Whenever you roll one or more dice, put a number of charge counters on Vexing Puzzlebox equal to the result.
{T}: Add one mana of any color. Roll a d20.
{T}, Remove 100 charge counters from Vexing Puzzlebox: Search your library for an artifact card, put that card onto the battlefield, then shuffle.

Chromatic Lantern

Lands you control have "{T}: Add one mana of any color."
{T}: Add one mana of any color.

Manor Gate

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

Maze's End

Maze's End enters tapped.
{T}: Add {C}.
{3}, {T}, Return Maze's End to its owner's hand: Search your library for a Gate card, put it onto the battlefield, then shuffle. If you control ten or more Gates with different names, you win the game.

Navigation Orb

{2}, {T}, Sacrifice Navigation Orb: Search your library for up to two basic land cards and/or Gate cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Hold the Gates

Creatures you control get +0/+1 for each Gate you control and have vigilance.

Doors of Durin

Whenever you attack, scry 2, then you may reveal the top card of your library. If it's a creature card, put it onto the battlefield tapped and attacking. Until your next turn, it gains trample if you control a Dwarf and hexproof if you control an Elf.

Sea Gate

Sea Gate enters tapped.
As Sea Gate enters, choose a color other than blue.
{T}: Add {U} or one mana of the chosen color.

The Surgical Bay

The Surgical Bay enters tapped.
{T}: Add {U}.
{1}{U}, {T}, Sacrifice The Surgical Bay: Draw a card.

Reshape

As an additional cost to cast this spell, sacrifice an artifact.
Search your library for an artifact card with mana value X or less, put it onto the battlefield, then shuffle.

Nine-Fingers Keene

Menace
Ward—Pay 9 life.
Whenever Nine-Fingers Keene deals combat damage to a player, look at the top nine cards of your library. You may put a Gate card from among them onto the battlefield. Then if you control nine or more Gates, put the rest into your hand. Otherwise, put the rest on the bottom of your library in a random order.

The Hunter Maze

The Hunter Maze enters tapped.
{T}: Add {G}.
{1}{G}, {T}, Sacrifice The Hunter Maze: Draw a card.

Faeburrow Elder

Vigilance
Faeburrow Elder gets +1/+1 for each color among permanents you control.
{T}: For each color among permanents you control, add one mana of that color.

Snow-Covered Plains

Sunbird Effigy

Flying, vigilance, haste
Sunbird Effigy's power and toughness are each equal to the number of colors among the exiled cards used to craft it.
{T}: For each color among the exiled cards used to craft Sunbird Effigy, add one mana of that color.

Sunbird Standard

{T}: Add one mana of any color.
Craft with one or more {5} ({5}, Exile this artifact, Exile one or more other permanents you control and/or cards from your graveyard: Return this card transformed under its owner's control. Craft only as a sorcery.)

Sunbird Standard // Sunbird Effigy

Gateway Sneak

Whenever a Gate you control enters, Gateway Sneak can't be blocked this turn.
Whenever Gateway Sneak deals combat damage to a player, draw a card.

Ubul Sar Gatekeepers

When Ubul Sar Gatekeepers enters, if you control two or more Gates, target creature an opponent controls gets -2/-2 until end of turn.

Sunspire Gatekeepers

When Sunspire Gatekeepers enters, if you control two or more Gates, create a 2/2 white Knight creature token with vigilance.

Orazca Puzzle-Door

{1}, {T}, Sacrifice Orazca Puzzle-Door: Look at the top two cards of your library. Put one of those cards into your hand and the other into your graveyard.

Opal Lake Gatekeepers

When Opal Lake Gatekeepers enters, if you control two or more Gates, you may draw a card.

Giant Trap Door Spider

{1}{R}{G}, {T}: Exile Giant Trap Door Spider and target creature without flying that's attacking you.

Gateway Shade

{B}: Gateway Shade gets +1/+1 until end of turn.
Tap an untapped Gate you control: Gateway Shade gets +2/+2 until end of turn.

Glinting Creeper

Converge — Glinting Creeper enters with two +1/+1 counters on it for each color of mana spent to cast it.
Glinting Creeper can't be blocked by creatures with power 2 or less.

Gatebreaker Ram

Gatebreaker Ram gets +1/+1 for each Gate you control.
As long as you control two or more Gates, Gatebreaker Ram has vigilance and trample.

Guild Summit

When Guild Summit enters, you may tap any number of untapped Gates you control. Draw a card for each Gate tapped this way.
Whenever a Gate you control enters, draw a card.

Alloy Myr

Open the Gates

Search your library for a basic land card or Gate card, reveal it, put it into your hand, then shuffle.

Gond Gate

Gates you control enter untapped.
{T}: Add {C}.
{T}: Add one mana of any color that a Gate you control could produce.

Selesnya Guildgate

Selesnya Guildgate enters tapped.
{T}: Add {G} or {W}.

Armory Guard

Armory Guard has vigilance as long as you control a Gate.

The Core

(Transforms from Matzalantli.)
Fathomless descent — {T}: Add X mana of any one color, where X is the number of permanent cards in your graveyard.

Matzalantli, the Great Door

{T}: Draw a card, then discard a card.
{4}, {T}: Transform Matzalantli, the Great Door. Activate only if there are four or more permanent types among cards in your graveyard. (Artifact, battle, creature, enchantment, land, and planeswalker are permanent types.)