msem-instigator

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

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.

Whenever a land you control enters, put a +1/+1 counter on Mountain Runt, then it deals 1 damage to up to one target creature you don't control.
When Mountain Runt has three or more +1/+1 counters on it, remove them all and transform it.

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

At the beginning of combat on your turn, put a +1/+1 counter on target creature you control. If that creature has flying, transform Mounting Up.

First strike
Whenever a creature dealt damage by Mournful Newborn this turn dies, transform Mournful Newborn.

Double strike

[+1]: Mpumo, Who Stands Alone deals 1 damage to any target and you gain 1 life.
[–X]: Exile target creature with mana value X.
[–6]: Choose up to four permanents an opponent controls. That player chooses one, then sacrifices the rest.

Whenever you tap a land for mana, add one mana of any type that land produced.
Whenever you cast a spell with mana value greater than the number of lands you control, sacrifice a land.

Sacrifice a creature or discard a card: Exile the top card of target player's library. You may cast that card for as long as it remains exiled. Any player may activate this ability but only once each turn and only during their turn.
You and permanents you control have hexproof from spells that were exiled with Mr. Jackston or that share a name with a card exiled with Mr. Jackston.

Deception {U}{B} ({U}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Ms. Moxie deals combat damage to a player, you may exile target nonland card with mana value 2 or less from your graveyard. If you do, cast a copy of that card without paying its mana cost.

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.

Trample, haste
Respawn (When this creature dies, if it attacked this turn, return it to its owner's hand.)
At the beginning of your end step, sacrifice a creature.

Trample
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.)

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.

[+1]: Up to one target creature gets +2/+0 until end of turn. Each player loses 1 life.
[–X]: Return target creature card with mana value X from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield.
[–7]: For each 1 life target player has less than their starting life total, create a 1/1 black Bird creature token with flying and deathtouch.

Look at the top three cards of your library, then put them into your graveyard or back on top of your library in any order.
Draw two cards.

Whenever a nontoken creature you control enters, if it shares no creature types with other creatures you control, draw a card.

Destroy target creature.

Whenever Murkriver Trawler attacks, until end of turn, target Rogue gains “Whenever this creature deals combat damage to a player, draw a card.”

Create two 1/1 white Soldier creature tokens. Prevent all damage that would be dealt to them this turn.

You may have Mutalithic Golem enter as a copy of any land on the battlefield, except it's an artifact in addition to its other types.

Reveal cards from the top of your library until you reveal a creature card and a land card. Put those cards into your hand and the rest on the bottom of your library in a random order.
Concord — If there are four or more card types among permanents you control, create two Treasure tokens.