Molten Echoes

As this enchantment enters, choose a creature type.
Whenever a nontoken creature you control of the chosen type enters, create a token that's a copy of that creature. That token gains haste. Exile it at the beginning of the next end step.

Genesis Chamber

Whenever a nontoken creature enters, if this artifact is untapped, that creature's controller creates a 1/1 colorless Myr artifact creature token.

Chaos Channeler

Wild Magic Surge — Whenever this creature attacks, roll a d20.
1—9 | Exile the top card of your library. You may play it this turn.
10—19 | Exile the top two cards of your library. You may play them this turn.
20 | Exile the top three cards of your library. You may play them this turn.

Tome of Legends

This artifact enters with a page counter on it.
Whenever your commander enters or attacks, put a page counter on this artifact.
{1}, {T}, Remove a page counter from this artifact: Draw a card.

Symmetry Matrix

Whenever a creature you control with power equal to its toughness enters, you may pay {1}. If you do, draw a card.

Decoction Module

Whenever a creature you control enters, you get {E} (an energy counter).
{4}, {T}: Return target creature you control to its owner's hand.

Ingenious Artillerist

Whenever one or more artifacts you control enter, this creature deals that much damage to each opponent.

Norin the Wary

When a player casts a spell or a creature attacks, exile Norin. Return it to the battlefield under its owner's control at the beginning of the next end step.

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.

Impact Tremors

Whenever a creature you control enters, this enchantment deals 1 damage to each opponent.

Heiko Yamazaki, the General

Trample
Whenever a Samurai or Warrior you control attacks alone, you may cast target artifact card from your graveyard this turn.

Hamletback Goliath

Whenever another creature enters, you may put X +1/+1 counters on this creature, where X is that creature's power.

Mycosynth Lattice

All permanents are artifacts in addition to their other types.
All cards that aren't on the battlefield, spells, and permanents are colorless.
Players may spend mana as though it were mana of any color.

Minion Reflector

Whenever a nontoken creature you control enters, you may pay {2}. If you do, create a token that's a copy of that creature, except it has haste and "At the beginning of the end step, sacrifice this permanent."

Witty Roastmaster

Alliance — Whenever another creature you control enters, this creature deals 1 damage to each opponent.

Mana Echoes

Whenever a creature enters, you may add an amount of {C} equal to the number of creatures you control that share a creature type with it.

Humble Defector

{T}: Draw two cards. Target opponent gains control of this creature. Activate only during your turn.

Cloudstone Curio

Whenever a nonartifact permanent you control enters, you may return another permanent you control that shares a permanent type with it to its owner's hand.

Pandemonium

Whenever a creature enters, that creature's controller may have it deal damage equal to its power to any target of their choice.

Ashnod's Altar

Embodiment of Flame

Whenever a spell you control deals damage, put a flame counter on this creature.
{1}, Remove a flame counter from this creature: Exile the top card of your library. You may play that card this turn.

Flame Channeler

When a spell you control deals damage, transform this creature.

Flame Channeler // Embodiment of Flame

Altar of the Brood

Whenever another permanent you control enters, each opponent mills a card.

Sizzling Soloist

Alliance — Whenever another creature you control enters, target creature an opponent controls can't block this turn. If this is the second time this ability has resolved this turn, that creature attacks during its controller's next combat phase if able.

Outpost Siege

As this enchantment enters, choose Khans or Dragons.
• Khans — At the beginning of your upkeep, exile the top card of your library. Until end of turn, you may play that card.
• Dragons — Whenever a creature you control leaves the battlefield, this enchantment deals 1 damage to any target.

Gonti's Aether Heart

Whenever Gonti's Aether Heart or another artifact you control enters, you get {E}{E} (two energy counters).
Pay eight {E}, Exile Gonti's Aether Heart: Take an extra turn after this one.

Mirror March

Whenever a nontoken creature you control enters, flip a coin until you lose a flip. For each flip you won, create a token that's a copy of that creature. Those tokens gain haste. Exile them at the beginning of the next end step.

Rose Room Treasurer

Alliance — Whenever another creature you control enters, create a Treasure token if this is the first or second time this ability has resolved this turn. Otherwise, you may pay {X}. When you do, this creature deals X damage to any target.

Devilish Valet

Trample, haste
Alliance — Whenever another creature you control enters, double this creature's power until end of turn.

Warstorm Surge

Whenever a creature you control enters, it deals damage equal to its power to any target.

Soultether Golem

Vanishing 1 (This creature enters with a time counter on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
Whenever another creature you control enters, put a time counter on this creature.

Bloodline Pretender

Changeling (This card is every creature type.)
As this creature enters, choose a creature type.
Whenever another creature you control of the chosen type enters, put a +1/+1 counter on this creature.

Foundry Street Denizen

Whenever another red creature you control enters, this creature gets +1/+0 until end of turn.

Kruin Striker

Whenever another creature you control enters, this creature gets +1/+0 and gains trample until end of turn. (It can deal excess combat damage to the player or planeswalker it's attacking.)

Confusion in the Ranks

Whenever an artifact, creature, or enchantment enters, its controller chooses target permanent another player controls that shares a card type with it. Exchange control of those permanents.

Vigilante Justice

Whenever a Human you control enters, this enchantment deals 1 damage to any target.

Purphoros, God of the Forge

Indestructible
As long as your devotion to red is less than five, Purphoros isn't a creature.
Whenever another creature you control enters, Purphoros deals 2 damage to each opponent.
{2}{R}: Creatures you control get +1/+0 until end of turn.

Electropotence

Whenever a creature you control enters, you may pay {2}{R}. If you do, that creature deals damage equal to its power to any target.