msem-instigator

Return target creature card with mana value 3 or less from your graveyard to the battlefield.
Fabled {4}{W}{W} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that creature.)

Mortal Tapestry gets +1/+1 for each land card in your graveyard.
Revive {4}{G} ({4}{G}, Exile this card from your graveyard: Create a token that's a copy of it except it has no mana cost. Revive only as a sorcery.)

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.

{B}{G}{U}: Mother Roo gets +2/+2 and gains flying until end of turn.

Flying
When Mother of Owls dies, you may return target creature an opponent controls to its owner's hand.

Whenever a creature dies, put a +1/+1 counter on Mother's Disciples.

(Transform this if it's not attached to a creature. Pay {3}{R}{R} as a sorcery to unattach it.)
Enchant creature you control
Mount of the Order's rider gets +5/+4.
{2}{R}: Target creature can't block Mount of the Order's rider this turn.

{4}{G}: Monstrosity 2. (If this creature isn't monstrous, put two +1/+1 counters on it and it becomes monstrous.)
When Mountain Bighorn becomes monstrous, you may have it fight target creature you don't control.

When Mountain-Western Inventor enters, you may return target artifact card from your graveyard to your hand.
{1}, Sacrifice an artifact: Target creature can't block or be blocked this turn.

Creatures you control get +2/+2 and gain first strike until end of turn.

First strike, haste
When Mounted Marksman enters, it deals 2 damage to target creature you don't control.

Whenever another nontoken creature you control enters, you may exile a number of cards from your graveyard equal to its mana value. If you do, create a token that's a copy of it, except the token isn't legendary if the creature is legendary.
{1}{B/G}: Look at the top card of your library. You may put that card into your graveyard.

Scry 2, then reveal the top or bottom card of your library. Creatures you control get +X/+X until end of turn, where X is that card's mana value.
Draw a card.

Menace
Whenever Msuji Operative deals combat damage to a player, reveal the top card of your library, put it into your hand, then you lose life equal to its mana value unless you discard a card.

As an additional cost to cast this spell, pay {3} or discard a card.
Respawn (When this creature dies, if it attacked this turn, return it to its owner's hand.)

When Mukal Reaper enters, you draw a card and you lose 2 life.
Respawn (When this creature dies, if it attacked this turn, return it to its owner's hand.)

Whenever Mukal Sire or another Construct you control enters, Mukal Sire deals 1 damage to each opponent.
Respawn (When this creature dies, if it attacked this turn, return it to its owner's hand.)

When Mukal Swarmhorde enters, put a +1/+1 counter on each other Construct you control.
Respawn (When this creature dies, if it attacked this turn, return it to its owner's hand.)

Respawn (When this creature dies, if it attacked this turn, return it to its owner's hand.)
Whenever Mukal Warleader attacks, the next Construct spell you cast this turn costs {1} less to cast.

When Mul Daya Elder enters, search your library for a basic land card, put it onto the battlefield tapped, then shuffle.
Whenever a land you control enters, put a +1/+1 counter on Mul Daya Elder.

As an additional cost to cast this spell, exile a creature card from your graveyard.
Create a tapped 2/3 black Mummy creature token.

Whenever a creature with flying attacks you, gain control of that creature at end of combat.

Enchant creature
Whenever enchanted creature attacks, it gets +3/+3 and gains trample until end of turn.

Destroy target creature an opponent controls, then that player sacrifices a creature.

({T}: Add {G} or {U}.)
As Mushroom Lagoon enters, you may pay {1}. If you don't, Mushroom Lagoon enters tapped.