msem-instigator

Whenever another nontoken permanent you control enters, create a Food token.
At the beginning of each end step, put X +1/+1 counters on up to one target creature, where X is the amount of life you've gained this turn.

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

Flying
Harrier's Falcon can't attack or block alone.

When Harvest Blighter enters, create a black Aura Curse enchantment token named Rotting Away attached to target player. The token has enchant player and “Whenever a creature enters under enchanted player's control, if it has toughness 2 or greater, put a -1/-1 counter on that creature.”

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.)

Whenever another creature you control enters, you may gain 1 life.
Whenever a creature enters under an opponent's control, you may have that player lose 1 life.

When Hashiro's Vanguard enters, each player sacrifices a nontoken creature.

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.

When Haunted Hermit enters, choose one —
• Put a +1/+1 counter on Haunted Hermit.
• Create a 1/1 white Spirit creature token with flying.

Flying
Whenever Haunting Horseman deals combat damage to a player, that player discards a card.

Flying
Cadence (Whenever you cast a spell, if its mana value is greater than this creature's power, put a +1/+1 counter on this creature.)

Trample
Whenever you cast a noncreature spell, crystallize. If you create a Treasure this way, Heartforge Savant deals 1 damage to you for each Treasure you've created this turn. (Put a +1/+1 counter on a creature you control or create a Treasure.)

Reach

Flying
When Heaven's Eyes enters, create a 1/1 white Bird creature token with flying. Then you gain 1 life for each creature in Heaven's Eyes's pack. (Two or more creatures you control with equal power are in a pack.)

Flying
{T}, Tap another untapped creature in Heaven's Gale Harrier's pack: Tap target creature. (Two or more creatures you control with equal power are in a pack.)

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
Whenever this creature attacks, if it's merged with another card or token, it deals 2 damage to target player or planeswalker.

Flying (This creature can't be blocked except by creatures with flying or reach.)
Heavensent Emissary enters with a +1/+1 counter on it for each other creature with flying you control.

Lifelink
Embellish {2}{B} (If you cast this spell for {2}{B}, create a 1/1 blue Thopter artifact creature token with flying when it enters.)

When Heirloom Seeker enters, you may search your library for an Equipment card, reveal it, then shuffle and put that card on top of it.
Heirloom Seeker has first strike as long as it's equipped.

Infiltrate (Whenever one or more attacking creatures you control aren't blocked, this creature gets +1/+1 until end of turn.)
Other creatures you control have infiltrate.

Flying, lifelink, haste
At the beginning of the end step, sacrifice Helix Entity.

Haste
The first instant or sorcery spell you cast each turn costs {1} less to cast.
{R}, {T}, Sacrifice Hellspark Prankster: Change the target of target spell with a single target.

Lifelink

Whenever a Project you control enters, create two 1/1 colorless Construct artifact creature tokens.
Whenever a creature leaves the battlefield, you may put a progress counter on a Project you control.