msem-instigator

Mossvine Lurker has trample as long as it has a +1/+1 counter on it.

Vigilance, reach, trample

When Moth-Heart Husk dies, create a 1/1 black Spirit creature token with flying.
Revive {3}{B} ({3}{B}, Exile this card from your graveyard: Create a token that's a copy of this card, except it has no mana cost. Activate this ability only any time you could cast a sorcery.)

Deathtouch
Other creatures you control get -1/-1.
Whenever Mother Night attacks, put target creature card from a graveyard onto the battlefield under your control.

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

Flying
Whenever another creature you control enters, you gain 1 life.

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.

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.

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.

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.

When Mourners of Mervin enters, you may sacrifice a creature or enchantment. If you do, creatures you control get +1/+1 and gain vigilance until end of turn.

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

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.

Players can't get counters.
Counters can't be put on permanents.

Double strike

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.

[+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.