msem-instigator

Whenever Halford enters or attacks, an opponent chooses one. When they choose one that has already been chosen, copy that ability.
• That opponent loses 2 life and you gain 2 life.
• That opponent sacrifices a permanent.
• That opponent discards a card. If they can't, draw a card.

{T}: Add {C}.
{3}, {T}, Sacrifice Hall of Random Access Memories: Return target artifact, instant, or sorcery card from your graveyard to your hand.

Enchant player
Creature tokens enchanted player controls get +1/+1.

{T}: Add {C}.
{T}: Add one mana of any color. Activate only if you have a counter.

Equipped creature gets +2/+2.
Whenever equipped creature attacks, until your next turn, up to one target creature can't attack or block and its activated abilities can't be activated.
Equip {2}

When Hand of Dominion enters, tap target creature an opponent controls. It doesn't untap during its controller's next untap step.
At the beginning of your upkeep, if your fealty to Islands is five or greater, transform Hand of Dominion. (Each Island you control counts towards your fealty to Islands.)

Flying
Whenever Hand of Genesis deals combat damage to a player, manifest the bottom card of your library. (To manifest a card, put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)

Whenever an artifact you control enters, look at the top card of your library. If that card's mana value is less than or equal to that artifact's mana value, you may reveal it and put that card into your hand. Otherwise, put it on the top or bottom of your library.

Indestructible
Whenever Hannaru the Conqueror attacks, put a +1/+1 counter on each creature you control.

When Hannaru's Spear enters, create Hannaru's Aegis, a legendary white Equipment artifact token with “Equipped creature gets +1/+2 and has vigilance” and equip {2}.
Equipped creature gets +2/+1 and has first strike.
Equip {2}

Flying, trample
Whenever Hao'Tai, the Ancient One deals combat damage to a player, exile the top four cards of that player's library. Until end of turn, you may cast instant, sorcery, and creature cards from among those exiled cards, and you may spend mana as though it were mana of any color to cast them.

If one or more counters would be put on a permanent you control, you may have that many counters plus one or that many counters minus one put on that permanent instead.

Flying
At the beginning of your first main phase, you may put any number of land cards from your hand onto the battlefield, then draw a card for each land put onto the battlefield this way.

When Harbinger of Growth enters, create a 1/1 green Saproling creature token.
{1}{G}, Sacrifice Harbinger of Growth: Populate. (Create a token that's a copy of a creature token you control.)

Whenever one or more Rogues you control attack, you may pay 1 life. If you do, draw a card.

When Hardened Explorer enters, choose one —
• Destroy target artifact.
• Put a +1/+1 counter on Hardened Explorer. It gains haste.

The next 2 damage that a source of your choice would deal to you and/or permanents you control this turn is dealt to any target instead.

As you cast instant and sorcery spells this turn, they gain “Draw a card” and “This spell deals 1 damage to any target.”

{2}, {T}: Target opponent exiles a nonland, nontoken permanent they control.
{2}, {T}: Put target permanent card exiled with Harmony Array onto the battlefield under your control.

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.

When a creature you control scavenges Harvest Reaper, search your library for a colorless card, reveal it, put it into your hand, then shuffle.
Scavenge {4} ({4}, 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.)

When Hate-Driven Arsonist enters, you may have it deal X damage to target creature or planeswalker, where X is the number of instant and sorcery cards in your graveyard.

Each player discards their hand, then draws cards equal to the greatest number of cards discarded this way.

Reprise {3}{R} (As you cast an instant or sorcery spell, you may exile one card with reprise from your graveyard and pay its reprise cost. If you do, add its effects to that spell.)
Hatsuo's Maneuver deals 1 damage to any target. Create a number of 1/1 red Warrior creature tokens equal to the damage dealt by this spell.

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