msem-instigator

Flying
Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
At the beginning of combat on your turn, if you're in a renaissance, target creature gains flying until end of turn.

Trample

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.

Flying, haste
At the beginning of each of your postcombat main phases, you may cast an instant or sorcery card from your graveyard with mana value less than or equal to the number of creatures that dealt combat damage to opponents this turn without paying its mana cost. If that spell would be put into a graveyard, exile it instead.

When Horizon Treader enters, exile target enchantment you control, then return that card to the battlefield under your control.

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.)

Flying
When Horned Spy enters, look at target player's hand.

No more than two creatures can attack each combat.

You may put a permanent card from your hand onto the battlefield.
Rerun (If you cast this from your hand, exile it as it resolves. Whenever a creature you control dies, you may cast this card from exile without paying its mana cost.)

Trample
Whenever Horrific Progenitor deals damage to a player, for each damage dealt, that player loses 3 life unless they sacrifice a nonland permanent or discard a card.

Return up to one target permanent card and up to one target Horror card from your graveyard to your hand.

Pressure {3}{B} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
Return target creature card from your graveyard to your hand. If this spell was cast for its pressure cost, put that card onto the battlefield instead.

Haste
When Horse Thief enters, you may gain control of target creature or Steed until end of turn. It gains haste until end of turn. If it's a Steed, attach it to Horse Thief.

Flying, lifelink

When Host of Nature enters, create two 2/2 red and green Elk creature tokens.

Whenever you cast a noncreature spell, any number of target creatures you control get +1/+1 until end of turn.
Whenever a creature you control deals an amount of combat damage exactly equal to its mana value to a player or planeswalker, draw a card.

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

Flying
When Hostile Barbfly enters, you may have it consume. When you do, target creature gets -2/-2 until end of turn. (To consume, sacrifice another creature or exile a creature card from your graveyard.)

Hostile Habitat deals 2 damage to each creature.
Leitmotif (If you cast this spell from your hand, exile it as it resolves. When you next cast a spell that shares a color with this card, you may cast this from exile without paying its mana cost.)

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.

This spell costs {3} less to cast if a permanent you controlled advanced this turn.
Gain control of target creature until end of turn. Untap it. It gains haste until end of turn.