msem-instigator

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.

This spell costs {3} less to cast if a creature died this turn.
Hatefire deals 6 damage to target creature or planeswalker. If that creature or planeswalker would die this turn, exile it instead.

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.

Haughty Chateau enters tapped unless you have two or more opponents.
{T}: Add {W} or {B}.

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

{T}: Add {C}.
{T}, Pay 1 life: Add {B} or {G}.

Haunted Estate enters tapped unless another player controls a land that could produce {W} or {B}.
{T}: Add {W} or {B}.

{T}: Add {C}.
{T}, Reappropriate: Add {U} or {R}. (Exile exactly two cards from your hand and/or graveyard.)

When Haunted Heirloom dies, create a Treasure token.

Haunted Hovel enters tapped.
{T}: Add {W} or {B}.
When Haunted Hovel enters, you may put a loyalty counter on a planeswalker you control.

{T}, Pay 1 life: Add {W} or {U}.
{2}, {T}, Sacrifice Haunted Manor and another permanent: Draw a card. Activate only during your turn.

Haunted Woodlock enters tapped unless you have two or more opponents.
{T}: Add {B} or {G}.

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.)

Hazy Coppice enters tapped.
{T}: Add {U} or {B}.
{2}{U}{B}: Until end of turn, Hazy Coppice becomes a 4/4 blue and black Bird creature with with flying and “Whenever this creature attacks or blocks, torment yourself.” It's still a land. (To torment yourself, lose 3 life unless you discard a card or sacrifice a nonland permanent.)

{T}, Sacrifice Hazy Lagoon: Search your library for a Plains or Island card and put it onto the battlefield tapped, then shuffle.

({T}: Add {U} or {B}.)
Hazy Moorland enters tapped.
Cycling {2} ({2}, Discard this card: Draw a card.)

Hazy Summits enters tapped.
{T}: Add {R} or {W}.
{1}, {T}: Add one mana of any color.

Menace
At the beginning of your end step, He of All Hallow's Eve deals damage equal to its power to you unless you're horrific. (You're horrific as long as you've sacrificed a permanent or discarded a card this turn.)

At the beginning of your end step, exile target permanent.
When Head of Ulko leaves the battlefield, return each other card exiled with it to the battlefield under your control.

Head on Collision deals 2 damage to any target.
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.)

When Healing Center enters, you gain 2 life.
{T}: Add {C}.