msem-instigator

When Automated Blademaster enters the battlefield, create a colorless Equipment artifact token named Sword with “Equipped creature gets +1/+1” and equip {1} and attach it to Automated Blademaster.

Reach
When Automated Overwatch enters the battlefield, create a Function token with “If this spell would create one or more tokens, it creates twice that many of those tokens instead.” (It's an enchantment. As you cast an instant or sorcery spell, sacrifice any number of Functions to add their effects to that spell.)

When Autumnal Resonants enters the battlefield, harmonize. (Trigger up to one harmony of a permanent you control.)
Harmony — Create a 3/3 red and green Elemental creature token with haste.

Trample
Harmony — Avalanche Drummer deals 1 damage to any target.
When Avalanche Drummer enters the battlefield, harmonize. (Trigger up to one harmony of a permanent you control.)

Deathtouch
Tribute 3 (As this creature enters the battlefield, an opponent of your choice may put three +1/+1 counters on it.)
When Avatar of Amosis enters the battlefield, if tribute wasn't paid, you may destroy target creature.

This spell costs {1} less to cast for each artifact and/or enchantment you control.
When Avatar of Innovations enters the battlefield, you may return target artifact or enchantment card from your graveyard to your hand.

When Avaz Banner enters the battlefield, attach it to target creature you control.
Equipped creature gets +2/+2 and is a Soldier Army in addition to its other types.
Equip {3}

First strike
When Avaz Cataphract enters the battlefield, judge another target creature you control. (Honor it by putting a +1/+1 counter on it or condemn it by sacrificing it to draw a card.)

Flying
Harmony — Until the end of your next turn, you may cast target instant or sorcery card from your graveyard. If that card would be put into your graveyard, exile it instead.
When Aven Acoustimancer enters the battlefield, harmonize. (Trigger up to one harmony of one permanent you control.)

Flying
When Aven Merchant enters the battlefield, create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

Flying
When Aven Strategist enters the battlefield, return up to one target creature to its owner's hand.

Enchant creature
When Awash in Despair enters the battlefield, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

When Awoken Animus enters the battlefield, create two 1/1 colorless Shapeshifter creature tokens with changeling. (They're every creature type.)
{2}, Discard Awoken Animus: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.

When Ayala's Blessing enters the battlefield, put a +1/+1 counter on up to two target creatures.
Whenever an embattled creature you control dies, you may return it to its owner's hand. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

Menace
When Azuma Hashiro, the Thronebreaker enters the battlefield, you may cast up to two cards from your opponents' graveyards without paying their mana costs. If those spells would be put into a graveyard, exile that card instead.

When Azure Archaeologist enters the battlefield, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)
{2}, {T}, Sacrifice a Clue: Draw two cards, then discard a card.

When Azutahn Hydromancer enters the battlefield, you may return target creature with power X or less to its owner's hand, where X is the number of differently named lands you control.

When Babyscale Bruiser enters the battlefield, you may reveal a creature card from your hand. If you do, Babyscale Bruiser deals damage to target creature an opponent controls equal to the revealed card's power. That creature deals damage equal to its power to Babyscale Bruiser.

When Backstage Broken enters the battlefield, create a 1/1 colorless Construct Actor creature token.
Whenever a token you control leaves the battlefield, you gain 1 life.

Deathtouch
When Backstage Comic enters the battlefield, target player discards a card.

When Backstage Tinkers enters the battlefield, you may return an artifact card from your graveyard to your hand.

When Backwoods Cultivator enters the battlefield, put a +1/+1 counter on target creature you control.
When Backwoods Cultivator dies, proliferate. (You choose any number of permanents and/or players with counters on them, then give each another kind of a counter already there.)

When Bal's Descent enters the battlefield, each player sacrifices a creature, discards two cards, and mills three cards.
{1}{B}{B}: Transform Bal's Descent. Activate only if your fealty to Swamps is five or greater. (Each Swamp you control counts towards your fealty to Swamps.)

This spell costs {U} less to cast if you dealt combat damage to a player this turn with a Rogue.
Flying
When Balloon Voyager enters the battlefield, draw a card.

Engorge (As this enters the battlefield, mill three cards, then exile a card from among the milled cards.)
When Bane of Sanity enters the battlefield, if it engorged a creature card, target player discards two cards.