Case of the Locked Hothouse

You may play an additional land on each of your turns.
To solve — You control seven or more lands. (If unsolved, solve at the beginning of your end step.)
Solved — You may look at the top card of your library any time, and you may play lands and cast creature and enchantment spells from the top of your library.

Dionus, Elvish Archdruid

Elves you control have "Whenever this creature becomes tapped during your turn, untap it and put a +1/+1 counter on it. This ability triggers only once each turn."

Heroic Intervention

Permanents you control gain hexproof and indestructible until end of turn.

Kodama's Reach

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.

Deathcap Glade

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

Harald, King of Skemfar

Menace (This creature can't be blocked except by two or more creatures.)
When Harald enters, look at the top five cards of your library. You may reveal an Elf, Warrior, or Tyvar card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Sword of the Paruns

As long as equipped creature is tapped, tapped creatures you control get +2/+0.
As long as equipped creature is untapped, untapped creatures you control get +0/+2.
{3}: You may tap or untap equipped creature.
Equip {3}

Prowess of the Fair

Whenever another nontoken Elf is put into your graveyard from the battlefield, you may create a 1/1 green Elf Warrior creature token.

Wirewood Channeler

{T}: Add X mana of any one color, where X is the number of Elves on the battlefield.

Hunter of Eyeblights

When this creature enters, put a +1/+1 counter on target creature you don't control.
{2}{B}, {T}: Destroy target creature with a counter on it.

Quest for Renewal

Whenever a creature you control becomes tapped, you may put a quest counter on this enchantment.
As long as there are four or more quest counters on this enchantment, untap all creatures you control during each other player's untap step.

Blessed Respite

Target player shuffles their graveyard into their library. Prevent all combat damage that would be dealt this turn.

Lothlórien Blade

Whenever equipped creature attacks, it deals damage equal to its power to target creature defending player controls.
Equip Elf {2}
Equip {5}

Staff of Domination

{1}: Untap this artifact.
{2}, {T}: You gain 1 life.
{3}, {T}: Untap target creature.
{4}, {T}: Tap target creature.
{5}, {T}: Draw a card.

Priest of Titania

{T}: Add {G} for each Elf on the battlefield.

Arcane Signet

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

Elven Chorus

You may look at the top card of your library any time.
You may cast creature spells from the top of your library.
Creatures you control have "{T}: Add one mana of any color."

Tyvar the Bellicose

Whenever one or more Elves you control attack, they gain deathtouch until end of turn.
Each creature you control has "Whenever a mana ability of this creature resolves, put a number of +1/+1 counters on it equal to the amount of mana this creature produced. This ability triggers only once each turn."

Sol Ring

Bojuka Bog

This land enters tapped.
When this land enters, exile target player's graveyard.
{T}: Add {B}.

Ruthless Winnower

At the beginning of each player's upkeep, that player sacrifices a non-Elf creature of their choice.

Elven Ambush

Create a 1/1 green Elf Warrior creature token for each Elf you control.

Prowler's Helm

Equipped creature can't be blocked except by Walls.
Equip {2}

Nadier, Agent of the Duskenel

Whenever a token you control leaves the battlefield, put a +1/+1 counter on Nadier.
When Nadier leaves the battlefield, create a number of 1/1 green Elf Warrior creature tokens equal to its power.
Partner (You can have two commanders if both have partner.)

Reliquary Tower

You have no maximum hand size.
{T}: Add {C}.

Craterhoof Behemoth

Haste
When this creature enters, creatures you control gain trample and get +X/+X until end of turn, where X is the number of creatures you control.

Golgari Rot Farm

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

Elvish Archdruid

Other Elf creatures you control get +1/+1.
{T}: Add {G} for each Elf you control.

Lys Alana Huntmaster

Whenever you cast an Elf spell, you may create a 1/1 green Elf Warrior creature token.

Casualties of War

Choose one or more —
• Destroy target artifact.
• Destroy target creature.
• Destroy target enchantment.
• Destroy target land.
• Destroy target planeswalker.

Joraga Warcaller

Multikicker {1}{G} (You may pay an additional {1}{G} any number of times as you cast this spell.)
This creature enters with a +1/+1 counter on it for each time it was kicked.
Other Elf creatures you control get +1/+1 for each +1/+1 counter on this creature.

Elfhame Sanctuary

At the beginning of your upkeep, you may search your library for a basic land card, reveal that card, put it into your hand, then shuffle. If you do, you skip your draw step this turn.

Marwyn, the Nurturer

Whenever another Elf you control enters, put a +1/+1 counter on Marwyn.
{T}: Add an amount of {G} equal to Marwyn's power.

Poison-Tip Archer

Reach (This creature can block creatures with flying.)
Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
Whenever another creature dies, each opponent loses 1 life.

Cultivate

Elvish Promenade

Wirewood Lodge

{T}: Add {C}.
{G}, {T}: Untap target Elf.

Timberwatch Elf

{T}: Target creature gets +X/+X until end of turn, where X is the number of Elves on the battlefield.

Woodland Cemetery

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

Circle of Dreams Druid

{T}: Add {G} for each creature you control.

Eladamri, Lord of Leaves

Other Elf creatures have forestwalk. (They can't be blocked as long as defending player controls a Forest.)
Other Elves have shroud. (They can't be the targets of spells or abilities.)

Beast Whisperer

Whenever you cast a creature spell, draw a card.

Elvish Warmaster

Whenever one or more other Elves you control enter, create a 1/1 green Elf Warrior creature token. This ability triggers only once each turn.
{5}{G}{G}: Elves you control get +2/+2 and gain deathtouch until end of turn.

Wolverine Riders

At the beginning of each upkeep, create a 1/1 green Elf Warrior creature token.
Whenever another Elf you control enters, you gain life equal to its toughness.

Nullmage Shepherd

Tap four untapped creatures you control: Destroy target artifact or enchantment.

Gilt-Leaf Palace

As this land enters, you may reveal an Elf card from your hand. If you don't, this land enters tapped.
{T}: Add {B} or {G}.

Kindred Summons

Choose a creature type. Reveal cards from the top of your library until you reveal X creature cards of the chosen type, where X is the number of creatures you control of that type. Put those cards onto the battlefield, then shuffle the rest of the revealed cards into your library.

Assassin's Trophy

Destroy target permanent an opponent controls. Its controller may search their library for a basic land card, put it onto the battlefield, then shuffle.

Dwynen, Gilt-Leaf Daen

Reach (This creature can block creatures with flying.)
Other Elf creatures you control get +1/+1.
Whenever Dwynen attacks, you gain 1 life for each attacking Elf you control.

Jagged-Scar Archers

Jagged-Scar Archers's power and toughness are each equal to the number of Elves you control.
{T}: This creature deals damage equal to its power to target creature with flying.

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control. It can attack and {T} no matter when it came under your control.)
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Imaryll, Elfhame Elite

Whenever Imaryll attacks, it gets +X/+X until end of turn, where X is the number of other Elves you control.
You may have Imaryll assign its combat damage as though it weren't blocked.

Necroblossom Snarl

As this land enters, you may reveal a Swamp or Forest card from your hand. If you don't, this land enters tapped.
{T}: Add {B} or {G}.

Elvish Champion

Other Elf creatures get +1/+1 and have forestwalk. (They can't be blocked as long as defending player controls a Forest.)

Galadhrim Ambush

Create X 1/1 green Elf Warrior creature tokens, where X is the number of attacking creatures.
Prevent all combat damage that would be dealt this turn by non-Elf creatures.

Golgari Locket

{T}: Add {B} or {G}.
{B/G}{B/G}{B/G}{B/G}, {T}, Sacrifice this artifact: Draw two cards.

Golgari Charm

Choose one —
• All creatures get -1/-1 until end of turn.
• Destroy target enchantment.
• Regenerate each creature you control.

Command Tower

Tainted Wood

{T}: Add {C}.
{T}: Add {B} or {G}. Activate only if you control a Swamp.

Immaculate Magistrate

{T}: Put a +1/+1 counter on target creature for each Elf you control.

Ezuri, Renegade Leader

{G}: Regenerate another target Elf.
{2}{G}{G}{G}: Elf creatures you control get +3/+3 and gain trample until end of turn.

Shaman of the Pack

When this creature enters, target opponent loses life equal to the number of Elves you control.

Door of Destinies

As this artifact enters, choose a creature type.
Whenever you cast a spell of the chosen type, put a charge counter on this artifact.
Creatures you control of the chosen type get +1/+1 for each charge counter on this artifact.

Patchwork Banner

As this artifact enters, choose a creature type.
Creatures you control of the chosen type get +1/+1.
{T}: Add one mana of any color.

Moldervine Reclamation

Whenever a creature you control dies, you gain 1 life and draw a card.

Swamp

Undergrowth Stadium

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

Twilight Mire

{T}: Add {C}.
{B/G}, {T}: Add {B}{B}, {B}{G}, or {G}{G}.

Path of Ancestry

This land enters tapped.
{T}: Add one mana of any color in your commander's color identity. When that mana is spent to cast a creature spell that shares a creature type with your commander, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Crown of Skemfar

Enchant creature
Enchanted creature gets +1/+1 for each Elf you control and has reach.
{2}{G}: Return this card from your graveyard to your hand.

Elderfang Venom

Attacking Elves you control have deathtouch.
Whenever an Elf you control dies, each opponent loses 1 life and you gain 1 life.

Skemfar Shadowsage

When this creature enters, choose one —
• Each opponent loses X life, where X is the greatest number of creatures you control that have a creature type in common.
• You gain X life, where X is the greatest number of creatures you control that have a creature type in common.

Elvish Guidance

Enchant land
Whenever enchanted land is tapped for mana, its controller adds an additional {G} for each Elf on the battlefield.

Llanowar Wastes

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

Tyvar Kell

Elves you control have "{T}: Add {B}."
+1: Put a +1/+1 counter on up to one target Elf. Untap it. It gains deathtouch until end of turn.
0: Create a 1/1 green Elf Warrior creature token.
−6: You get an emblem with "Whenever you cast an Elf spell, it gains haste until end of turn and you draw two cards."

Myriad Landscape

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

The Cauldron of Eternity

This spell costs {2} less to cast for each creature card in your graveyard.
Whenever a creature you control dies, put it on the bottom of its owner's library.
{2}{B}, {T}, Pay 2 life: Return target creature card from your graveyard to the battlefield. Activate only as a sorcery.

Lathril, Blade of the Elves

Menace (This creature can't be blocked except by two or more creatures.)
Whenever Lathril deals combat damage to a player, create that many 1/1 green Elf Warrior creature tokens.
{T}, Tap ten untapped Elves you control: Each opponent loses 10 life and you gain 10 life.

Three Tree City

As Three Tree City enters, choose a creature type.
{T}: Add {C}.
{2}, {T}: Choose a color. Add an amount of mana of that color equal to the number of creatures you control of the chosen type.

Yavimaya, Cradle of Growth

Each land is a Forest in addition to its other land types.

Rogue's Passage

{T}: Add {C}.
{4}, {T}: Target creature can't be blocked this turn.

Abomination of Llanowar

Vigilance; menace (This creature can't be blocked except by two or more creatures.)
Abomination of Llanowar's power and toughness are each equal to the number of Elves you control plus the number of Elf cards in your graveyard.