msem-instigator

When Master of Marble Row enters, choose one —
• Create a colorless Monument artifact token with “Creatures you control get +1/+1.”
• Create a white Cloister enchantment token with “When this enchantment enters, exile target nonland permanent an opponent controls until this enchantment leaves the battlefield.”

You may activate equip abilities any time you could cast an instant if you pay an additional {1} to activate them.
Armed — Equipped creatures you control get +1/+1 as long as Master of Steel is equipped.

Flying (This creature can't be blocked except by creatures with flying or reach.)
Whenever Master of Winds or another creature with flying you control enters, you may draw a card.

When Master of the Glen enters, create a 2/2 green Wolf Elemental creature token.
Elementals you control have trample.

Menace (This creature can't be blocked except by two or more creatures.)
Whenever Mausoleum Revenant deals damage to a player, create a 2/2 black Zombie creature token.

Creatures you control lose poisonous and can't have or gain poisonous.
Snakes you control deal damage to players in the form of poison counters.

Poisonous 3 (Whenever this creature deals combat damage to a player, that player gets three poison counters.)
At the beginning of your upkeep, if an opponent is poisoned, you may have Mautakesh Strangler fight target creature you don't control.

As long as you control another white creature, Mavisa's Familar has lifelink. The same is true for blue and flying, black and deathtouch, and red and trample.

Breach (Whenever this deals combat damage to a player, you may have it become an Aura Curse until your next turn. Attach it to that player.)
Recursive — As long as Mayar, Nullcrowned is a Curse, they have all nonrecursive abilities of other Curses and creatures with breach you control.
Pay 3 life: Target enchantment creature gains haste and menace until end of turn.

Your opponents can't gain life.
If a source you control would deal damage to an opponent, it deals double that damage instead.
At the beginning of your end step, if Mayhem Tandem didn't attack this turn, transform it.

Lifelink, menace

Whenever Mei's Student deals combat damage to a player, fateseal 1, then scry 1. (Look at the top card of an opponent's library, then you may put it on the bottom.)

Melodae, the Favored can't be blocked by black creatures.
If Melodae would be destroyed, instead sacrifice a creature and Melodae gains indestructible until end of turn.

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.

When Memory Figment is put into your graveyard from your hand or library, you may exile it. If you do, for as long as it remains exiled, you may cast it. It costs {2} less to cast this way.

Whenever Memory of Fatalism dies or you cast a noncreature spell, each opponent loses 2 life and you gain 2 life.
{4}: Put Memory of Fatalism from your graveyard on top of your library.

Flash
Flying
When Mending Valkyrie enters, choose target permanent you own or permanent card with mana value 3 or less in your graveyard. You may return it to your hand.

Adorned — Mercenary Lancer gets +2/+2 as long as it's equipped and/or enchanted.

Armed — Merciless Brute gets +2/+2 as long as it's equipped.

Merciless Champion can't block unless you control another Knight or Soldier.

Menace
Ferocious — Whenever Merciless Xun Huang attacks, if you control a creature with power 4 or greater, defending player sacrifices a permanent.

{1}{U}: Mercurial Merfolk gets +2/-2 until end of turn.
When Mercurial Merfolk dies, draw a card.

Improve {1}{G/U} ({1}{G/U}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
You may play an additional land on each of your turns.
Wanderlust — At the beginning of your end step, if you control four or more differently named lands, you may draw a card.

Flying, haste
{X}{R}{R}, Exile an instant or sorcery card with mana value X from your graveyard: Return Merkurio's Familiar from your graveyard to the battlefield. It gets +X/+0 until end of turn.

Survivors you control get +3/+3.