msem-instigator

When Lifespark Alchemist enters, create a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)
Whenever Lifespark Alchemist or another creature dies, each opponent loses 1 life.

Lifelink
Whenever an opponent searches one or more libraries, they lose 2 life.
Attain {4}{B} ({4}{B}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

When Lotus Wastes Survivalist enters, target player discards a card. Create a Treasure token unless a nonland card was discarded this way.

When Maghbri Whisper enters, nourish 1. (To nourish 1, either put a +1/+1 counter on this creature or create a 1/1 white Citizen creature token.)
Sacrifice a creature: Maghbri Whisper gets +2/+2 until end of turn.

Menace
When Marrow Raptor enters, you may sacrifice a land or exile a land card from your graveyard. If you do, put a +1/+1 counter on it.

Marrowskitter can't block and can't be blocked.
{3}{B}{B}: Return Marrowskitter from your graveyard to the battlefield. Create a token that's a copy of it.

If you would create an Army token while Mehr's Unending Horde is in your graveyard, you may instead return Mehr's Unending Horde from your graveyard to the battlefield.
Counters remain on Mehr's Unending Horde as it moves to any zone other than a player's hand or library.

Flash
When Mennin Pack enters, each opponent loses 1 life.
When Mennin Pack dies, each opponent discards a card.

Whenever Merciless Bandit or another creature you control dies, each opponent loses 1 life and you gain 1 life.

Deathtouch
When Nel Toth Shaman enters, mill two cards.

{U/B}{U/B}: Return Nherix, the Soulcage from your graveyard to the battlefield tapped.
{6}: Return target creature card with mana value 2 or less from your graveyard to the battlefield tapped.

Menace
Ni'Ama's Emissary gets +1/+1 as long as you control a red or white permanent.

Flying (This creature can't be blocked except by creatures with flying or reach.)
{B}: Night Screecher gains deathtouch until end of turn. (Any amount of damage this deals to a creature is enough to destroy it.)

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
{T}: Salvage a creature card. (Exile one from your graveyard until this creature leaves the battlefield. Whenever this creature deals combat damage to a player, put a card it salvaged into your hand.)

When Ominous Presence enters, search your library for a Curse card, reveal it, then shuffle. If it has mana value 4 or less, you may put it onto the battlefield. Otherwise, put it into your hand.
Ominous Presence gets +1/+1 for each Curse attached to your opponents.

Whenever Ontarachie Hunter attacks, each opponent loses 1 life.
At the beginning of your end step, if an opponent has 10 or less life, transform Ontarachie Hunter.

Ward—Pay 2 life.
When Orchid Suit enters, target opponent reveals their hand, then exiles a nonland card of their choice from it until Orchid Suit leaves the battlefield.

{T}: Target player loses 1 life.
Whenever you cast a spell from your graveyard, untap Paincaller.

{1}, Discard a card: Painted Watcher gets +1/+1 and becomes the color of your choice until end of turn.

Sacrifice a creature: Pale Horse gets +2/+2 until end of turn.
Ride {B} ({B}: Transform this and attach it to target creature you control without a Steed. Ride only as a sorcery.)

At the beginning of your upkeep, you may pay {U}. If you do, return Persistent Fiend from your graveyard to your hand.

Deathtouch
When Pestilent Scavenger enters, you may mill three cards.

Deathtouch
Whenever Phantasmal Stalker deals damage to a planeswalker, destroy it.

Deathtouch

When Ravenous Rats enters, target opponent discards a card.