msem-instigator

{W}: Target creature assigns combat damage equal to its toughness rather than its power this turn.

Whenever Haunted Prodigy attacks, you may tap target creature.
Unveil {2}{W}{U} ({2}{W}{U}: Transform this. Unveil only as a sorcery.)

Vigilance
At the beginning of your end step, if you control two or more Spirits and/or creatures with flying, transform Haunted Waif.

Whenever Haunting Maestro attacks, you may tap or untap up to two target creatures.

Flying
Whenever Havengul Banshee attacks, each creature defending player controls gets -1/-0 until end of turn.
{3}{U}: Return Havengul Banshee from your graveyard to the battlefield transformed under your control attached to target opponent. Activate only as a sorcery.

Ward—Sacrifice a permanent.
Whenever a player sacrifices a permanent, put a +1/+1 counter on Hayat, Hungering Bakhtak.
Surpass {4}{B}{G} ({4}{B}{G}: Transform this creature. This costs {1} less to activate for each counter on it. Activate only as a sorcery.)

Deathtouch
Discard a card: Headless Carriage gains indestructible until end of turn. Tap it.
Ride {2}{B}{B} ({2}{B}{B}: Transform this and attach it to target creature you control without a Steed. Ride only as a sorcery.)

Flying, vigilance, deathtouch, lifelink

Enchant creature
When Heartstrings leaves the battlefield, exile enchanted creature.
Whenever enchanted creature attacks or blocks, exile it at end of combat.

Lifelink

(Transform this if it's not attached to a creature. Pay {B} as a sorcery to unattach it.)
Enchant creature you control
Herald of Death's rider gets +1/+1.
Sacrifice a creature: Herald of Death's rider gets +2/+2 until end of turn.

Whenever you put a counter on another permanent you control, put a +1/+1 counter on Herald of Ruination. This ability triggers only once each turn.
Surpass {5}{G} ({5}{G}: Transform this creature. This costs {1} less to activate for each counter on it. Activate only as a sorcery.)

(Transform this if it's not attached to a creature. Pay {4}{G} as a sorcery to unattach it.)
Enchant creature you control
Herdstrider's rider gets +1/+1 for each land you control and has trample.
Whenever Herdstrider's rider attacks, create an X/X green Elephant creature token with trample that's tapped and attacking, where X is that creature's power. Exile that token at the end of combat.

Target player sacrifices any number of lands. That player searches their library for up to that many land cards, puts them onto the battlefield tapped, then shuffles.
Fabled {5}{G}{G} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that player.)

Lifelink
Tap three other untapped creatures and/or artifacts you control: Transform Heroic Crusader.

Whenever you cast a spell that's white, blue, black, or green, put a +1/+1 counter on Hesitant Vanguard.
Surpass {5}{R} ({5}{R}: Transform this creature. This costs {1} less to activate for each counter on it. Activate only as a sorcery.)

Scry 2, then create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)
Monument {2}{R} (You may cast this transformed from your graveyard for its monument cost. Exile it if it would leave the battlefield or not resolve.)

{T}, Sacrifice Hidden Garden Entrance: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.
Monument {W}{U}{B}{R}{G} (You may cast this transformed from your graveyard for its monument cost. Exile it if it would leave the battlefield or not resolve.)

Target creature gains flying and gets +1/+0 for each card in your hand until end of turn.
Fuse (You may cast one or both halves of this card from your hand.)

Flash
When Highpoint Guru enters, scry X, where X is the number of Monks you control.

Flying, lifelink

Highpoint Shrine enters tapped unless you played it from exile.
{T}: Add {W} or {U}.

Create X 1/1 blue Boar Dragon creature tokens with flying. (Then exile this card. You may cast the creature later from exile.)

When Hoof Cliff Caretaker enters, return target card of an opponent's choice from your graveyard to your hand.

Trample, haste