msem-instigator

Search your library for up to two basic land cards, put them onto the battlefield tapped, then shuffle. Put a +1/+1 counter on each creature you control.

Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
{3}{G}: Harmonic Recruit gets +2/+2 until end of turn. If you're in a renaissance, it gets +4/+4 until end of turn instead.

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

Ferocious — Whenever a creature with power 4 or greater you control enters, you gain 4 life.

Harpoon Launching deals 3 damage to any target. Create a 1/1 red Goblin creature token.

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.

When Harried Submersible enters, target opponent creates a 1/1 blue Tentacle creature token.
Whenever Harried Submersible deals combat damage to a player or planeswalker, draw a card.
Crew 2 (Tap any number of creatures you control with total power 2 or greater: This Vehicle becomes an artifact creature until end of turn.)

As an additional cost to cast this spell, sacrifice a land.
Search your library for up to two basic land cards, put them onto the battlefield, then shuffle.

Destroy target colorless nonbasic permanent. Harsh Erosion deals 2 damage to that permanent's controller.

Enchant creature
Enchanted creature gets +2/+0 and has haste.

Cast this spell only during your turn and only during the declare attackers step or with its acquiesce ability.
Untap all creatures you control. After this phase, there is an additional combat phase.
Acquiesce (If you cast this spell from your hand, exile it as it resolves. When one or more creatures you control deal combat damage to an opponent, you may cast this card from exile without paying its mana cost.)

Enchant land
Whenever enchanted land is tapped for mana, its controller adds one mana of any color.

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.)

At the beginning of your upkeep, Harvest the Stars deals 4 damage to any target.

Harvest (You may tap any number of creatures you control as you cast this spell. If you do, reduce this spell's mana cost by their total power.)
Create a 5/5 colorless Scarecrow artifact creature token with “This creature can't block or harvest.”
Flashback {8}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Discard your hand. Creatures you control get +X/+0 and gain first strike until end of turn, where X is the number of cards discarded this way.

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.

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

Whenever you cast a spell during an opponent's turn, Haughty Priest deals 1 damage to that player.

When Haunted Heirloom dies, create a Treasure token.

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever another noncreature source deals damage to a creature or player, you may have Hav'za, Itavan Warchief deal half that damage, rounded up, to any target.

Haste (This creature can attack and {T} as soon as it comes under your control.)
Mirage {R} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)