msem-instigator

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Whenever Mistress of Frost extorts a spell, you may tap target artifact or creature.

Misty Churchyard enters tapped.
{T}: Add {W}.
{1}{W}{W}: Until end of turn, Misty Churchyard becomes a 1/4 Cleric creature with “Whenever this creature is dealt damage, put that many +1/+1 counters on it.” Activate only if you're horrific.

You may play Molten Basin from your graveyard as long as seven or more cards are in your graveyard.
Molten Basin enters tapped.
{T}: Add {B} or {R}.
Cycling {1}{B}{R} ({1}{B}{R}, Discard this card: Draw a card.)

({T}: Add {B} or {R}.)
Molten Falls enters tapped.
{1}, {T}: Add {B}{B} or {R}{R}.

Molten Mire enters tapped unless you control a basic land.
{T}: Add {B} or {R}.

({T}: Add {G} or {U}.)
Monsoon Lagoon enters tapped.
Cycling {2} ({2}, Discard this card: Draw a card.)

{T}: Add {R} or {G}. You lose 1 life unless you have less life than an opponent.

{T}: Add {C}.
{4}: Put a +1/+1 counter on Monument of Queens. You may have it become a 0/0 Avatar creature with flying, first strike, vigilance, trample, and lifelink until end of turn. It's still a land.

({T}: Add {B}.)
Moon of the Encroaching Night enters tapped.
{1}{B}, {T}: Scry 1.

({T}: Add {W}.)
Moon of the Final Dawn enters tapped.
{1}{W}, {T}: Scry 1.

({T}: Add {U}.)
Moon of the Frozen Dusk enters tapped.
{1}{U}, {T}: Scry 1.

({T}: Add {R}.)
Moon of the Lingering Day enters tapped.
{1}{R}, {T}: Scry 1.

({T}: Add {G}.)
Moon of the Promised Day enters tapped.
{1}{G}, {T}: Scry 1.

Moonchaser Meadow enters tapped.
{T}: Add {W}.
{1}{W}{W}, {T}: Put a loyalty counter on each planeswalker you control.

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.

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

Prowess, trample
When this creature transforms into Mortal Frame, add {R}{R}{R}.

Mortal Realms enters tapped unless you control two or more other lands.
{T}: Add {R}.
{T}, Pay 1 life: Add {B} or {G}.

Puzzlebox (Begin the game with this and another card you own from outside the game in the command zone, locked. That card is face down until you unlock this.)
{3}: Unlock Mortal's Conundrum. If the revealed card is black, put it into your hand. Otherwise, put it on top of your library.
At the beginning of your upkeep, if Mortal's Conundrum is unlocked, you lose 2 life.

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.

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

Experience (Whenever this creature attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)

(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.