msem-instigator

As Moonlight Sanctum enters, choose Waxing or Waning.
• Waxing — At the beginning of your upkeep, you gain 1 life for each enchantment you control.
• Waning — Nonenchantment spells cost {1} more to cast.

First strike
Other Harpies you control get +1/+1 and have first strike.
Whenever a Harpy you control dies, put a +1/+1 counter on Moonlight Stalker.

Moonlit Shore enters tapped unless you control two or more blue and/or black permanents.
{T}: Add {U} or {B}.

{T}: Add {C}.
{T}, Exile two cards from your graveyard: Add {U} or {B}.

Moonshard Crater enters tapped.
{T}: Add {R}.
{2}{R}, {T}: Each player sacrifices a nonbasic land.

Once each turn, when another nontoken creature is returned to your hand from the battlefield, you may create a token that's a copy of that creature.

At the beginning of your upkeep, you may put a reinforcement counter on Moranai Paragon.
Whenever Moranai Paragon attacks, you may put a creature card with mana value equal to the number of reinforcement counters on Moranai Paragon from your hand onto the battlefield.

Whenever Morbid Mimic enters or attacks, exile up to one target creature card from a graveyard.
Morbid Mimic has all activated abilities of cards exiled with it.

Flying
Whenever another creature you control attacks, you may pay {1}. If you do, put a +1/+1 counter on it.

Lifelink
Whenever Morning's Warden becomes the target of a spell or ability an opponent controls, exile target creature that player controls.

Morningstar Blaze deals X damage divided as you choose among one or two targets.

{T}: Add {C}.
{1}, {T}, Sacrifice Morphic Verge: Choose two different basic land types. Create a colorless land token that's the chosen types.

Target opponent mills five cards, then you exile up to two instant and/or sorcery cards from that player's graveyard. You may cast those cards for as long as they remain exiled, and you may spend mana as though it were mana of any type to cast them.

Choose up to one target land card and up to one target creature card with mana value 3 or less from your graveyard. Return one to the battlefield and the rest to your hand.

Exile target creature or planeswalker, then exile its controller's graveyard.

Gain control of target creature until end of turn.
Coalesce {6}{U}{B} (You may cast this from your graveyard for {6}{U}{B}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)
As long as Mortal Whims Falter is on the battlefield, you can't lose control of permanents.

Players can't gain life.
At the beginning of each player's upkeep, if that player has 10 or less life, they lose 1 life.

Whenever Mortified Medium or another creature enters, you gain 1 life.
As long as you have at least 10 life more than your starting life total, Mortified Medium gets +4/+4 and has flying.

Flying
{1}{W/U}{W/U}: Creatures you control gain flying until end of turn if another creature you control has flying. The same is true for first strike, double strike, deathtouch, haste, indestructible, lifelink, menace, reach, trample, and vigilance.

Mosecf, the Sunseeker's Path enters tapped.
Whenever a creature you control attacks, put a creation counter on Mosecf.
{T}, Remove ten creation counters from Mosecf and sacrifice it: Creatures you control get +2/+2 and gain vigilance until end of turn. Activate only as a sorcery.

Vigilance, reach, trample

({T}: Add {B} or {G}.)
Mossy Shrine enters tapped unless you control two or more basic lands.

Whenever you sacrifice a permanent, you may put a -1/-1 counter on target creature.

Codex — Leyran Alpha, Fungal Whomper, Plated Crusher, Towering Hydraffe, The Terror of Shady Cove. (As this enters, conjure its contents into a shuffled face-up additional library.)
When Mother of Monsters enters, you gain 6 life.
When Mother of Monsters dies, draw a card.

(Transform this if it's not attached to a creature. Pay {1}{W} as a sorcery to unattach it.)
Enchant creature you control
Mount of Heroes's rider gets +2/+1.
Sacrifice Mount of Heroes: Counter target spell that targets you or Mount of Heroes's rider.