msem-instigator

{T}, Pay 1 life: Add {G} or {U}.
{1}, {T}, Sacrifice Hidden Hollow: Investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Whenever a player casts a spell, that player reveals cards from the top of their library until they reveal two land cards, then puts all cards revealed this way into their graveyard.

When Hideaway Agent enters, gain control of target nonland permanent with mana value 3 or less for as long as you control Hideaway Agent.

At the beginning of your upkeep, if you control a legendary creature, you draw a card and you lose 1 life.

Flash
Prowess
When High Rollers Esteemed enters, you may choose new targets for target spell or ability unless its controller has High Rollers Esteemed deal 4 damage to them.

Lifelink
Triggered abilities of creatures you control that would trigger only when that creature enters instead trigger whenever you gain life for the first time each turn.

Whenever Highpeak Rider attacks, search your library for a land card and put it onto the battlefield, then shuffle. Sacrifice that land at the beginning of the next end step.

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

This spell can't be countered.
Enchant land
At the beginning of combat on your turn, untap enchanted land. It becomes a 6/6 green Lizard creature with haste until end of turn. It's still a land.

When Himari enters, put a +1/+1 counter on a creature you control.
Creatures you control with counters on them have base power and toughness 4/4 and have trample.

Equipped creature gets +2/+2.
Whenever equipped creature attacks, draw a card. Noncreature spells you cast this turn can be cast as though they had flash.
Equip {2}

(Activate each ability only once as a sorcery. You gain the realm's favor after activating them all.)
{W}: Put a first strike counter on target creature.
{1}{W}: Invigorate 2. (Choose a creature with the least power among creatures you control and put two +1/+1 counters on it.)
{2}{W}: Create two 1/1 white Soldier creature tokens.
Creatures you control with counters on them have flying and lifelink.

When Hinode, the Sacred Summit enters, draw a card, then choose a creature card name.
Creatures you control with the chosen name have flying, vigilance, and lifelink.

Destroy all creatures and planeswalkers with mana value X or less.

{2}{R}, {T}, Exert Hinterland Ritualist, Sacrifice another creature: Hinterland Ritualist deals damage equal to the sacrificed creature's power to any target. Activate only as a sorcery. (An exerted creature won't untap during your next untap step.)

When Hirukari's Immortal dies, if it didn't enter this turn, create a token that's a copy of it, except it has no mana cost.

When Hitana's Implements enters, draw a card.
{1}, {T}: Add one mana of any color.
Augmented — At the beginning of each end step, if you've spent {W}{U}{B}{R}{G} on spells this turn, exile Hitana's Implements. If you do, create a 5/5 blue Horror creature token.

At the beginning of your upkeep, each opponent mills cards equal to the number of card types among permanents you control.

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

Reveal the top three cards of your library. Put up to one creature or Revelation card from among them into your hand and the rest into your graveyard.
Coalesce {6}{G} (You may cast this from your graveyard for {6}{G}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)
Hold Life in Taloned Grasp's power is equal to the number of cards in your graveyard.

As Holdsteady Engine enters, choose a card name.
Cards with the chosen name entering the battlefield don't cause abilities to trigger.
Activated abilities of cards with the chosen name can't be activated unless they're mana abilities.

Trample
Hollow Survivor's power and toughness are each equal to the number of cards in your hand.
Whenever Hollow Survivor deals combat damage to a player, draw a card.

When Holy War enters, create three 1/1 white Cleric creature tokens.
Creature tokens you control have first strike and lifelink.

Return a permanent card from your graveyard to your hand.
Motley — If there are five or more names among nonland permanents you control, return two permanent cards from your graveyard to your hand instead.

While an opponent is choosing targets as part of casting a spell they control or activating an ability they control, that player must choose at least one Flagbearer on the battlefield if able.
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)