msem-instigator

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.)

Whenever another creature you control dies, put a +1/+1 counter on Marshy Marauder.
When Marshy Marauder dies, create a 1/1 green Insect creature token for each counter on it.

{T}: Add one mana of any color.

Whenever another creature you control enters, you may pay {2}. If you do, judge that creature. (Honor it by putting a +1/+1 counter on it or condemn it by sacrificing it to draw a card.)

{1}, Sacrifice Martyr of the Work: Purge. (Exile two cards that share a type from graveyards. If you do, draw a card.)

First strike

Sacrifice Masahita's Servant: Exile the top card of your library. Until end of turn, you may play that card.

At the beginning of your upkeep, exile the top card of your library. Masahita, Bloodtongue deals damage to you equal to that card's mana value. Until end of turn, you may play that card.

Spirited (When this creature enters, you may activate one of its activated abilities without paying its cost.)
{1}, {T}: Look at the top card of your library. You may put the card back or into your graveyard.

When Masha's Lightbound becomes tapped for the first time each turn, untap Masha's Lightbound and each other creature you control.
{W}, {T}: Exile target card from a graveyard.

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.

Whenever another creature enters, Masquerading Bohemian becomes a copy of that creature except it's a Noble in addition to its other types and it has this ability.

Instant and sorcery spells you cast cost {1} less to cast.
{U}, {T}, Exile three instant and/or sorcery cards from your graveyard: Draw a card.

Whenever a nonbasic nontoken land enters under an opponent's control, create a tapped colorless land token named Fading Rift with “{T}, Sacrifice this land: Add one mana of any color.”

You can't cast more than one spell each turn.
Whenever you cast a spell, draw a card.

Whenever an artifact you control enters, Master of Munitions deals 1 damage to each opponent.

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you cast a noncreature spell, you may switch Master of Tranquility's power and toughness until end of turn.

Enchant creature
Enchanted creature gets +1/+1.
{W}: Enchanted creature gains vigilance until end of turn.
{1}{W}: Enchanted creature gains first strike until end of turn.

(Add a quest counter as this enters. Sacrifice after 3.)
Whenever one or more creatures you control survive damage, add a quest counter.
1 — You may put a creature card with mana value 2 or less from your hand onto the battlefield.
2 — Put two +1/+1 counters on target creature you control.
3 — Choose target creature you control. You draw cards equal to half that creature's power, rounded down.

Flash
Reach
Whenever Mattia enters or becomes tapped, put a +1/+1 counter on target creature you control.
{2}{G}, {T}: Target creature must be blocked this turn if able. Activate only as a sorcery.

When Mausoleum Rite enters, each player mills four cards.
{2}{B}, Exile a creature card from your graveyard: Create an Idol token. (It's an artifact with “{1}, Sacrifice this artifact: Put a +1/+1 counter on target creature. Activate only as a sorcery.”)

When Mausoleum Suffragan enters, create a white and black Aura enchantment token named Pale Shroud attached to target creature. The token has enchant creature and “Enchanted creature gets +1/+1 and has lifelink.”
Whenever an artifact or enchantment you control enters, each opponent loses 1 life.

When Maven of Fear enters, mill two cards.
Maven of Fear gets +2/+1 and has menace as long as six or more cards are in your graveyard.

Alpha (You may have this creature enter with a +1/+1 counter on it. If you do, it becomes alpha and can only attack alone.)

Enchant creature you control
Whenever enchanted creature attacks, mill three cards.
When enchanted creature leaves the battlefield, create an X/X green Spirit creature token, where X is equal to the number of card types among cards in your graveyard.