msem-instigator

First strike, vigilance
Whenever Asamund, Queen of Yroncaster deals combat damage to a player, choose a number. That player can't cast noncreature spells with mana value equal to the chosen number until the end of your next turn.

Put any number of target creature cards from your graveyard on top of your library. You draw two cards and you lose 2 life.

Destroy target creature. Create a tapped Treasure token.

When Aureate Golem enters, create a Treasure token. Each other player creates a tapped Treasure token. (They're artifacts with “{T}, Sacrifice this artifact: Add one mana of any color.”)

When Awoken Animus enters, 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.

Equipped creature gets +3/+2.
Whenever a land you control enters, you may attach Axe of the Crann to target creature you control.
Equip {4}

The first instant or sorcery spell you cast each turn has convoke. (Each creature you tap while casting that spell pays for {1} or one mana of that creature's color.)

Put two +1/+1 counters on target creature. Untap that creature.

Backstabbing Courtiers can't attack unless you foretold a card or cast a foretold spell this turn.

Whenever Backstreet Gutter-Runner attacks, if you control another Pirate or Rogue, it deals 2 damage to each opponent.

Prowess
Whenever Balefire Conjurer attacks, you may pay {1}{R}. If you do, exile the top card of your library. You may play that card until the end of your next turn.

Whenever Baljurn, the Runelord or another nontoken artifact or enchantment you control enters, create a 0/0 blue Construct artifact creature token. Put a +1/+1 counter on each artifact and/or enchantment creature you control other than Baljurn.

Choose one —
• Destroy target artifact or enchantment.
• Barkcrush deals 5 damage to target creature with flying.

Put a +1/+1 counter on each creature you control. Creature tokens you control gain vigilance until end of turn.

(Transform this if it's not attached to a creature. Pay {1}{U} as a sorcery to unattach it.)
Enchant creature you control
Bay-Bandit's Snapper's rider gets +1/+2.
Whenever Bay-Bandit's Snapper's rider deals combat damage to a player, you draw two cards.

All creatures that aren't embattled get -5/-5 until end of turn. If a creature would die this turn, exile it instead. (A creature is embattled if it has a counter on it or a permanent its owner controls attached to it.)

Whenever another creature you control dies, put a +1/+1 counter on Belligerent Mob.

(Transform this if it's not attached to a creature. Pay {2}{B}{B} as a sorcery to unattach it.)
Enchant creature you control
Belmord Blood-Coach's rider gets +3/+3 and has deathtouch.
Whenever Belmord Blood-Coach's rider attacks, you may return target creature card with mana value less than its rider's power from your graveyard to the battlefield tapped.

Blessed Barrage deals 5 damage divided as you choose among any number of attacking or blocking creatures.

Blighted Unicorn can't block.
Ride {3}{B} ({3}{B}: Transform this and attach it to target creature you control without a Steed. Ride only as a sorcery.)

Improve {1}{R} ({1}{R}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
As long as Bloodbelly Glutton is embattled, it has first strike, menace, and haste. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

Lifelink
{1}{B}, Sacrifice Bloodbond Ritualist: Look at the top three cards of your library. Put one of them into your hand and the rest into your graveyard.

When Bloodbriar Acolyte dies, draw a card. Each opponent loses 1 life.

Trample
{T}, Sacrifice another creature: You gain 3 life.
Whenever another creature you control dies, put a +1/+1 counter on Bloodbriar Archdruid.