msem-instigator

When Honey Pot enters, create two 1/1 black Demon enchantment creature tokens with breach and “This creature can't block.” (Whenever it deals combat damage to a player, you may have it become an Aura Curse until your next turn. Attach it to that player.)
Whenever a Curse you control becomes attached to an opponent, that player loses 1 life and you gain 1 life.

Renown 1 (When this creature deals combat damage to a player, if it isn't renowned, put a +1/+1 counter on it and it becomes renowned.)
Whenever a creature you control blocks or becomes blocked, it gets +1/+1 until end of turn for each +1/+1 counter on it.

Flying
Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)
Whenever Honorable Mentor mentors a creature, that creature and Honorable Mentor each gain first strike until end of turn.

Flying
Whenever a Harpy you control becomes the target of a spell, scry 1.

Other Angels and Nephilim you control get +1/+0.
{3}{W}: Until end of turn, Hooded Mystic becomes an Angel, gets +3/+3 and gains flying.

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

(Add a quest counter as this enters. Sacrifice after 3.)
Once each turn, when you cast a spell with mana value equal to the number of lands you control, you may add a quest counter.
You may search your library for a basic land card, reveal it, then shuffle and put that card on top. You gain 1 life for each quest counter on Hoof Cliff Expedition.
Search your library for a creature card, reveal it, put it into your hand, then shuffle.

Trample, haste

Double strike
When a creature you control scavenges Hook-Style Trainee, put a double strike counter on that creature.
Scavenge {4}{R} ({4}{R}, 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.)

Other Pirates you control get +1/+0.
Whenever another Pirate you control enters, Hookhand Freebooter deals 1 damage to any target.
When Hookhand Freebooter dies, create a Bullet token. (It's an artifact with “{T}, Sacrifice this artifact: It deals 1 damage to any target.)

Create a token that's a copy of target creature you control, except it has base power and toughness 2/2.
Retrace (You may cast this card from your graveyard by discarding a land card in addition to paying its other costs.)

Flying
Morph {4}{W} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When you turn Hopebringer Cherub face up, creatures you control get +1/+1 until end of turn.

When you attain Hopeless Lanonshee, create two 1/1 black Construct artifact creature tokens.
Whenever a creature dies, each opponent loses 1 life and you gain 1 life.

Whenever Hopeless Romantic or another creature you control dies, each opponent loses 1 life.
Attain {3}{B} ({3}{B}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Pressure {U} (You may cast this spell for its pressure cost if there are seven or more cards in your graveyard.)

Armed — Whenever Hordedriver Enthusiast attacks, if it's equipped, creatures you control get +1/+0 and gain trample until end of turn.

When Horizon Gazer enters, reveal the top two cards of your library. Put a noncreature card revealed this way into your hand and the rest into your graveyard.
Ascend {3}{G} ({3}{G}: Exile this creature, then return it to the battlefield transformed. Ascend only as a sorcery.)

Flying, vigilance
At the beginning of your end step, if a creature you control dealt combat damage to an opponent this turn, put a +1/+1 counter on Horizon Prophet.

Horizon Wayfarer's power and toughness are each equal to the number of differently named lands you control.

As Horizon of Origins enters, you may reveal an Island or Mountain card from your hand. If you don't, Horizon of Origins enters tapped.
{T}: Add {U} or {R}.

Trample
Harmony — Put a +1/+1 counter on target Warrior you control. You gain 1 life.
Whenever one or more Warriors you control deal combat damage to a player, harmonize. (Trigger up to one harmony of a permanent you control.)

When Horn of Seasons enters, search your library for a basic land card, put it onto the battlefield tapped, then shuffle.
Equipped creature gets +3/+0.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

Tap an untapped Desert you control: Hostile Atmosphere deals 1 damage to any target.

Alpha (You may have this creature enter with a +1/+1 counter on it. If you do, it becomes alpha and can only attack alone.)
Lifelink

Flash
When Hostile Takeover enters, you may counter target noncreature spell.
At the beginning of your upkeep, you may put a progress counter on a Project you control.