msem-instigator

Whenever you gain life for the first time each turn, reveal the top card of your library. If it's a land or creature card, put it into your hand. Otherwise, put it into your graveyard.

Menace
Whenever Margarete or another creature you control dies, up to one target creature you control cackles. (Put a menace counter on it. If it already has menace, it deals 1 damage to each opponent instead.)
Once each turn, when Margarete or another creature you control with menace dies, you may torment each opponent. (They lose 3 life unless they discard a card or sacrifice a nonland permanent.)

Haste
Rapport — Whenever Maghbri Hunter and at least one other creature you control become tapped, Maghbri Hunter gets +2/+1 until end of turn.

When Maghbri Whisper enters, nourish 1. (To nourish 1, either put a +1/+1 counter on this creature or create a 1/1 white Citizen creature token.)
Sacrifice a creature: Maghbri Whisper gets +2/+2 until end of turn.

Activated abilities of nonland permanents cost {2} more to activate.

{X}, {T}: Target player mills X cards.

Nonenchantment spells cost {1} more to cast.
Whenever you cast an enchantment spell, you gain 1 life and draw a card.

Prowess
When Maktali Visionary enters, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Dominance — When Mammoth Crab enters, draw a card if you control the creature with the greatest power or tied for the greatest power.

{T}: Add {C}.
{1}, {T}: Add one mana of any color.

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Whenever Manipulator of Waves attacks, mill three cards. Then create a 0/0 blue Elemental Serpent creature token with “This creature gets +1/+1 for each five cards in your graveyard.”

Marinton Occultist can't block or be blocked.
Whenever one or more cards are put into a player's graveyard from their library, Marinton Occultist gets +1/+1 until end of turn.

{T}: Draw a card, then discard a card. If you discarded an instant, sorcery, Pirate, or Rogue card this way, create a 1/1 blue Tentacle creature token with “This creature can't block.”

Defender
{1}{W}, {T}: Tap target creature.

Menace
When Marrow Raptor enters, you may sacrifice a land or exile a land card from your graveyard. If you do, put a +1/+1 counter on it.

Marrowskitter can't block and can't be blocked.
{3}{B}{B}: Return Marrowskitter from your graveyard to the battlefield. Create a token that's a copy of it.

Whenever you sacrifice one or more permanents, put a +1/+1 counter on Marsh Dweller.

When Marshal of Brethren enters, amass Soldiers 1. (Put a +1/+1 counter on an Army you control. It's also a Soldier. If you don't control one, create an 0/0 black Soldier Army creature token first.)

First strike
Whenever Martial Maestro attacks, other attacking creatures you control get +1/+0 until end of turn.

Trample
Whenever you cast a spell with more colors than the number of counters on Martoob Beastkeeper, put a +1/+1 counter on Martoob Beastkeeper.

{T}: Add one mana of any color.

Lionize {2}{U} ({2}{U}, Exile this card from your hand: Put a +1/+1 counter on target creature and it gains the following ability until end of turn. You may cast this card on a later turn from exile.)
Whenever this creature deals combat damage to a player, draw that many cards.

Whenever Masha's Vanguard deals damage to a player, you may put a creature card with mana value X or less from your hand onto the battlefield, where X is the amount of damage dealt this way.

Masked Impersonator can't be blocked.
Art of war — At the beginning of your end step, if Masked Impersonator dealt damage to an opponent this turn, you may have it become a copy of target creature you control except it has this ability.

Once each turn, when you activate a nonmana ability, you may have Masked Servant get +1/+1 until end of turn.
{2}{W}: Untap target creature.