msem-instigator

As Harlowe, Thespian Extraordinaire enters, choose a color and creature type.
Harlowe, Thespian Extraordinaire is the chosen color.
Harlowe, Thespian Extraordinaire is the chosen type in addition to its other types.

First strike
Whenever you discard a card, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Reach
Whenever one or more creatures with flying attack, harmonize. (Trigger up to one harmony of a permanent you control.)
Harmony — Harpstring Ranger gets +2/+2 until end of turn. Untap it.

Flying
Harrier's Falcon can't attack or block alone.

First mate—Your starting deck contains at least twelve Vehicles. (If this card outside the game is your chosen first mate, you may swap it with a card in your opening hand.)
Haste
{R}{W}, {T}: You may put a Vehicle card from your hand onto the battlefield. That Vehicle gains haste and becomes an artifact creature until end of turn.

Whenever an opponent activates an ability that isn't a mana ability, amass Soldiers 1 unless its controller pays {2}. (To amass Soldiers 1, put a +1/+1 counter on an Army you control. It's also a Soldier. If you don't control one, create a 0/0 black Soldier Army creature token first.)

When Harvest Blighter enters, create a black Aura Curse enchantment token named Rotting Away attached to target player. The token has enchant player and “Whenever a creature enters under enchanted player's control, if it has toughness 2 or greater, put a -1/-1 counter on that creature.”

Whenever Harvester of Secrets or another creature enters from your graveyard, you may draw a card.
Unearth {2}{U}{B} ({2}{U}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the end step or if it would leave the battlefield. Unearth only as a sorcery.)

Menace
Art of war — At the beginning of your end step, if Hashiro's Infiltrator dealt damage to an opponent this turn, that player discards a card.

When Hashiro's Vanguard enters, each player sacrifices a nontoken creature.

First strike
{1}{R}: Hatsuo, Honored General and other Warrior creatures you control get +1/+0 until end of turn.

When Haughty Paladin enters, you may sacrifice another artifact or creature. If you do, tap all creatures your opponents control.

When Haunted Heirloom dies, create a Treasure token.

{W}, Sacrifice Haunting Bard: Destroy target artifact or enchantment.

Flying
Whenever Haunting Horseman deals combat damage to a player, that player discards a card.

Scavenge {5}{U} ({5}{U}, Exile this card from your graveyard: Put a number of +1/+1 counters equal to this card's power on target creature. Scavenge only as a sorcery.)

Menace
When Heart of the Deadwood enters, destroy up to one target creature, then put up to one target creature card from a graveyard onto the battlefield under your control.

Menace
Sacrifice a Goblin: Heartless Warleader gets +2/+2 until end of turn.

Reach

Vigilance
{W}: Heaven's Champion gains first strike until end of turn.

Flying
When Heaven's End Chronicler enters, mill three cards, then choose three cards in your graveyard. An opponent separates them into two piles. Return one pile to your hand.

Whenever a creature in Heaven's Fire Ascetic's pack attacks, that creature deals 1 damage to defending player. (Two or more creatures you control with equal power are in a pack.)

Trial 3 (As you cast this spell, an opponent of your choice may pay 3 life. If they don't, they fail the trial.)
When Heedless Adversary enters, you may have it deal 3 damage to target creature if that creature's controller failed the trial.

When Heedless Lovers enters, you may return target Citizen card from your graveyard to your hand.
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.)

Lifelink
Embellish {2}{B} (If you cast this spell for {2}{B}, create a 1/1 blue Thopter artifact creature token with flying when it enters.)