Cultivate

Search your library for up to two basic land cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Dirtcowl Wurm

Whenever an opponent plays a land, put a +1/+1 counter on Dirtcowl Wurm.

Aether Sting

Whenever an opponent casts a creature spell, Aether Sting deals 1 damage to that player.

Shard Convergence

Search your library for a Plains card, an Island card, a Swamp card, and a Mountain card. Reveal those cards, put them into your hand, then shuffle.

Raiders' Wake

Whenever an opponent discards a card, that player loses 2 life.
Raid — At the beginning of your end step, if you attacked this turn, target opponent discards a card.

Ever-Watching Threshold

Whenever an opponent attacks, if they attacked you and/or a planeswalker you control, draw a card.

Deep-Sea Kraken

Deep-Sea Kraken can't be blocked.
Suspend 9—{2}{U} (Rather than cast this card from your hand, you may pay {2}{U} and exile it with nine time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost. It has haste.)
Whenever an opponent casts a spell, if Deep-Sea Kraken is suspended, remove a time counter from it.

Mogg Sentry

Whenever an opponent casts a spell, Mogg Sentry gets +2/+2 until end of turn.

Voice of Resurgence

Whenever an opponent casts a spell during your turn or when Voice of Resurgence dies, create a green and white Elemental creature token with "This creature's power and toughness are each equal to the number of creatures you control."

Decree of Silence

Whenever an opponent casts a spell, counter that spell and put a depletion counter on Decree of Silence. If there are three or more depletion counters on Decree of Silence, sacrifice it.
Cycling {4}{U}{U} ({4}{U}{U}, Discard this card: Draw a card.)
When you cycle Decree of Silence, you may counter target spell.

Mind's Eye

Whenever an opponent draws a card, you may pay {1}. If you do, draw a card.

Ghostly Pilferer

Whenever Ghostly Pilferer becomes untapped, you may pay {2}. If you do, draw a card.
Whenever an opponent casts a spell from anywhere other than their hand, draw a card.
Discard a card: Ghostly Pilferer can't be blocked this turn.

Soul Barrier

Whenever an opponent casts a creature spell, Soul Barrier deals 2 damage to that player unless they pay {2}.

Isolation Cell

Whenever an opponent casts a creature spell, that player loses 2 life unless they pay {2}.

Farseek

Search your library for a Plains, Island, Swamp, or Mountain card, put it onto the battlefield tapped, then shuffle.

Jeweled Lotus

{T}, Sacrifice Jeweled Lotus: Add three mana of any one color. Spend this mana only to cast your commander.

Wildfire Elemental

Whenever an opponent is dealt noncombat damage, creatures you control get +1/+0 until end of turn.

Cindervines

Whenever an opponent casts a noncreature spell, Cindervines deals 1 damage to that player.
{1}, Sacrifice Cindervines: Destroy target artifact or enchantment. Cindervines deals 2 damage to that permanent's controller.

Runic Armasaur

Whenever an opponent activates an ability of a creature or land that isn't a mana ability, you may draw a card.

Growth Spiral

Draw a card. You may put a land card from your hand onto the battlefield.

Lavinia, Azorius Renegade

Each opponent can't cast noncreature spells with mana value greater than the number of lands that player controls.
Whenever an opponent casts a spell, if no mana was spent to cast it, counter that spell.

Smothering Tithe

Whenever an opponent draws a card, that player may pay {2}. If the player doesn't, you create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Underworld Dreams

Whenever an opponent draws a card, Underworld Dreams deals 1 damage to that player.

Kaervek the Merciless

Whenever an opponent casts a spell, Kaervek the Merciless deals damage equal to that spell's mana value to any target.

Arasta of the Endless Web

Reach
Whenever an opponent casts an instant or sorcery spell, create a 1/2 green Spider creature token with reach.

Swamp

Ishai, Ojutai Dragonspeaker

Flying
Whenever an opponent casts a spell, put a +1/+1 counter on Ishai, Ojutai Dragonspeaker.
Partner (You can have two commanders if both have partner.)

Taurean Mauler

Changeling (This card is every creature type.)
Whenever an opponent casts a spell, you may put a +1/+1 counter on Taurean Mauler.

Scab-Clan Berserker

Haste
Renown 1 (When this creature deals combat damage to a player, if it isn't renowned, put a +1/+1 counter on it and it becomes renowned.)
Whenever an opponent casts a noncreature spell, if Scab-Clan Berserker is renowned, Scab-Clan Berserker deals 2 damage to that player.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice Commander's Sphere: Draw a card.

Myriad Landscape

Myriad Landscape enters the battlefield tapped.
{T}: Add {C}.
{2}, {T}, Sacrifice Myriad Landscape: Search your library for up to two basic land cards that share a land type, put them onto the battlefield tapped, then shuffle.

Ob Nixilis, the Hate-Twisted

Whenever an opponent draws a card, Ob Nixilis, the Hate-Twisted deals 1 damage to that player.
−2: Destroy target creature. Its controller draws two cards.

Lurking Predators

Whenever an opponent casts a spell, reveal the top card of your library. If it's a creature card, put it onto the battlefield. Otherwise, you may put that card on the bottom of your library.

Sunscorch Regent

Flying
Whenever an opponent casts a spell, put a +1/+1 counter on Sunscorch Regent and you gain 1 life.

Xyris, the Writhing Storm

Flying
Whenever an opponent draws a card except the first one they draw in each of their draw steps, create a 1/1 green Snake creature token.
Whenever Xyris, the Writhing Storm deals combat damage to a player, you and that player each draw that many cards.

Kraum, Ludevic's Opus

Flying, haste
Whenever an opponent casts their second spell each turn, draw a card.
Partner (You can have two commanders if both have partner.)

Nekusar, the Mindrazer

At the beginning of each player's draw step, that player draws an additional card.
Whenever an opponent draws a card, Nekusar, the Mindrazer deals 1 damage to that player.

Memory Erosion

Whenever an opponent casts a spell, that player mills two cards.

Mountain

Path to the World Tree

When Path to the World Tree enters the battlefield, search your library for a basic land card, reveal it, put it into your hand, then shuffle.
{2}{W}{U}{B}{R}{G}, Sacrifice Path to the World Tree: You gain 2 life and draw two cards. Target opponent loses 2 life. Path to the World Tree deals 2 damage to up to one target creature. You create a 2/2 green Bear creature token.

Kambal, Consul of Allocation

Whenever an opponent casts a noncreature spell, that player loses 2 life and you gain 2 life.

Lotus Field

Hexproof
Lotus Field enters the battlefield tapped.
When Lotus Field enters the battlefield, sacrifice two lands.
{T}: Add three mana of any one color.

Tovolar's Magehunter

Whenever an opponent casts a spell, Tovolar's Magehunter deals 2 damage to that player.
At the beginning of each upkeep, if a player cast two or more spells last turn, transform Tovolar's Magehunter.

Mondronen Shaman

At the beginning of each upkeep, if no spells were cast last turn, transform Mondronen Shaman.

Mondronen Shaman // Tovolar's Magehunter

Savai Triome

({T}: Add {R}, {W}, or {B}.)
Savai Triome enters the battlefield tapped.
Cycling {3} ({3}, Discard this card: Draw a card.)

Lotus Cobra

Landfall — Whenever a land enters the battlefield under your control, add one mana of any color.

Harrow

As an additional cost to cast this spell, sacrifice a land.
Search your library for up to two basic land cards, put them onto the battlefield, then shuffle.

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.

Immolation Shaman

Whenever an opponent activates an ability of an artifact, creature, or land that isn't a mana ability, Immolation Shaman deals 1 damage to that player.
{3}{R}{R}: Immolation Shaman gets +3/+3 and gains menace until end of turn.

Pain Magnification

Whenever an opponent is dealt 3 or more damage by a single source, that player discards a card.

Fate Unraveler

Whenever an opponent draws a card, Fate Unraveler deals 1 damage to that player.

The World Tree

The World Tree enters the battlefield tapped.
{T}: Add {G}.
As long as you control six or more lands, lands you control have "{T}: Add one mana of any color."
{W}{W}{U}{U}{B}{B}{R}{R}{G}{G}, {T}, Sacrifice The World Tree: Search your library for any number of God cards, put them onto the battlefield, then shuffle.

Sol Ring

Plains

Spelltithe Enforcer

Whenever an opponent casts a spell, that player sacrifices a permanent unless they pay {1}.

Forest

Reparations

Whenever an opponent casts a spell that targets you or a creature you control, you may draw a card.

Dragonlair Spider

Reach
Whenever an opponent casts a spell, create a 1/1 green Insect creature token.

Golos, Tireless Pilgrim

When Golos, Tireless Pilgrim enters the battlefield, you may search your library for a land card, put that card onto the battlefield tapped, then shuffle.
{2}{W}{U}{B}{R}{G}: Exile the top three cards of your library. You may play them this turn without paying their mana costs.

Jace, Unraveler of Secrets

+1: Scry 1, then draw a card.
−2: Return target creature to its owner's hand.
−8: You get an emblem with "Whenever an opponent casts their first spell each turn, counter that spell."

Predatory Hunger

Enchant creature
Whenever an opponent casts a creature spell, put a +1/+1 counter on enchanted creature.

Island

Command Tower

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

Harsh Mentor

Whenever an opponent activates an ability of an artifact, creature, or land on the battlefield, if it isn't a mana ability, Harsh Mentor deals 2 damage to that player.

Lone Wolf of the Natterknolls

Whenever an opponent casts a spell during your turn, draw two cards.
At the beginning of each upkeep, if a player cast two or more spells last turn, transform Lone Wolf of the Natterknolls.

Hermit of the Natterknolls

Whenever an opponent casts a spell during your turn, draw a card.
At the beginning of each upkeep, if no spells were cast last turn, transform Hermit of the Natterknolls.