msem-instigator

Flash
Reach
Whenever Mattia enters or becomes tapped, put a +1/+1 counter on target creature you control.
{2}{G}, {T}: Target creature must be blocked this turn if able. Activate only as a sorcery.

When Mausoleum Suffragan enters, create a white and black Aura enchantment token named Pale Shroud attached to target creature. The token has enchant creature and “Enchanted creature gets +1/+1 and has lifelink.”
Whenever an artifact or enchantment you control enters, each opponent loses 1 life.

When Maven of Fear enters, mill two cards.
Maven of Fear gets +2/+1 and has menace as long as six or more cards are in your graveyard.

This spell can't be countered.
Flying, haste
Mayu, the Endless Flow gets +2/+2 for each spell you've cast this turn.

Mechanized Ideal gets +X/+Y, where X is the highest base power among other creatures you control and Y is the highest base toughness among other creatures you control.

Artifact vision (Whenever this or another artifact you control enters, reveal the top card of your library. Then you may put that card into your graveyard.)
Whenever Mechanomind Researcher envisions an artifact card, put a +1/+1 counter on it.

Flying
{2/B}{2/B}, {T}, Sacrifice Meddling Gargoyle: Target opponent reveals their hand. You choose a nonland card from it. That player discards that card. Activate only as a sorcery.

Flying
When Mei's Understudy enters, if you control another Actor, draw a card.

Flash
Flying
When Meletis Stratomancer enters, target creature an opponent controls gets -2/-0 until end of turn.

Whenever Melodious Musician attacks, tap target creature an opponent controls.

Whenever Memoria Thief deals combat damage to a player, look at that player's hand. You may choose a nonland card from it. If you do, that player reveals the chosen card, puts it on the bottom of their library, then draws a card.

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.

When Merciless Blackguard enters, each player sacrifices a creature. For each creature token sacrificed this way, you may create a Treasure token.

Infiltrate (Whenever one or more attacking creatures you control aren't blocked, this creature gets +1/+1 until end of turn.)
Whenever Merciless Exiled deals combat damage to a player, scry 2.

{T}: Draw a card, then discard a card.

Motivate 1 (When this creature enters, you may motivate target creature with less power than this by putting a +1/+1 counter on it.)
When Merthilios' Escort motivates a creature, that creature gains first strike until end of turn.

Mianju enters with your choice of a menace or +1/+1 counter on them.
Whenever two or more creatures in Mianju's pack attack, mill three cards, then return a creature card from your graveyard to your hand. (Two or more creatures you control with equal power are in a pack.)

When Miede-District Alchemist enters, add {R}{R}{R}.
Paranoia {1}{R} (You may cast this spell for its paranoia cost when a permanent you control leaves the battlefield.)

Haste
{R}, {T}: Miede-District Enforcer deals 2 damage to target creature that entered this turn or player that cast a creature spell this turn.
Paranoia {1}{R} (You may cast this spell for its paranoia cost when a permanent you control leaves the battlefield.)

Ferocious — Whenever a creature with power 4 or greater you control enters, Mieng, Who Dances With Dragons becomes a 4/4 Dragon creature with flying until end of turn.

Whenever you gain life, Militant Youth gets +1/+1 until end of turn.

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
You may cast the first spell that's an enchantment, instant, or sorcery with mana value 1 you cast each turn without paying its mana cost.

Flying
Mind's Contagion has haste as long as there are two or more creature cards in your graveyard.
Whenever Mind's Contagion deals combat damage to a player, until your next turn, it gains “Noncreature spells opponents cast cost an additional 2 life to cast.”

Whenever you cast an instant or sorcery spell, target player mills a card.