msem-instigator

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.

Menace
Landfall — Whenever a land you control enters, Mawdryk's Elite gets +1/+0 and gains deathtouch until end of turn.

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.

Alpha (You may have this creature enter with a +1/+1 counter on it. If you do, it becomes alpha and can only attack alone.)

Lifelink, menace

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Whenever a marked creature dies, put a +1/+1 counter on Mei's Collector.

Flash
Flying
When Mellan enters, exile up to one other target nonland permanent with mana value equal to or less than the number of creatures you control with flying until Mellan leaves the battlefield.

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.

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.

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.

Menace

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

Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
{2}{B}, Discard a card: Mercenary of the Folded Fan gains indestructible until end of turn. Tap it. If you're in a renaissance, draw a card.

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

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.

Whenever Merfolk Vandal deals combat damage to a player, you may pay {U}. If you do, transform it.

Kicker {2} (You may pay an additional {2} as you cast this spell.)
Prowess
When Merkurio's Opus enters, if it was kicked, draw two cards, then discard two cards.

Survivors you control get +3/+3.

{T}: Add one mana of color.
{3}{G}, {T}: Audition for green. Activate only as a sorcery. (Create a 1/1 Construct Actor creature token, a Scout Role giving 2/3 and vigilance, or a Warrior Role giving 3/2 and trample. Roles replace older ones.)

Artifact spells you cast cost {1} less to cast.
{2}, Sacrifice an artifact: Target creature gains deathtouch until end of turn.

When Mettalia's Forward enters, you may salvage a 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.)

Mettalia is all colors.
Mettalia has protection from each color among cards she's salvaged in exile.
When Mettalia enters, for each color, you may salvage a nonlegendary card of that color. (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.)

Whenever a land you control enters, crystallize.
{10}: Shuffle any number of other permanents you control into their owner's library. Mill that many cards. Put all permanent cards milled this way onto the battlefield. Activate only during your turn and only once each turn.