msem-instigator

Create a token that's a copy of target creature you control.
Fabled {5}{U}{U} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that creature.)

Modular Mercenary gets +1/+0 and has first strike as long as you control a creature with a +1/+1 counter on it.

First strike, haste
When Moeru Thunderers enters, if it's not a token, create a token that's a copy of it, except it has no mana cost.

Flash
When Mokuteki Ambusher enters, until end of turn, other creatures you control gain “{T}: This creature deals 1 damage to any target.”

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
Double strike
If this creature would deal noncombat damage, it deals double that damage instead.

When Monk of Mid-Autumn enters, choose one —
• Put a double strike counter on Monk of Mid-Autumn.
• Destroy target artifact or enchantment.
• Monk of Mid-Autumn deals 2 damage to target tapped creature and you gain 2 life.

{T}: Add {G} or {U}.
{G}{U}, {T}: Return target creature you control to its owner's hand.

Vanguard — Whenever a creature you control attacks alone, that creature gets +3/+0 until end of turn.

Lifelink
At the beginning of your end step, you gain 1 life if you gained life this turn, and each opponent that lost life this turn loses 1 life.

Whenever you gain life, you may put target creature or planeswalker card from your graveyard on top of your library.

As Moonlight Sanctum enters, choose Waxing or Waning.
• Waxing — At the beginning of your upkeep, you gain 1 life for each enchantment you control.
• Waning — Nonenchantment spells cost {1} more to cast.

Flying
When Moonlit Charmer enters, tap target artifact or creature. It doesn't untap during its controller's next untap step.

Whenever Moonlit Lurker blocks, put a +1/+1 counter on it.

When Moonshadow Remnant enters, destroy target tapped creature.
Mirage {3}{W}{W} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)

Flying
{1}{U}: Reveal the top card of your library. Moonwing Watcher's base power becomes equal to that card's mana value.
Prophecy {U} (Once each turn, you may exile a card with prophecy as you reveal it. When you do, you may cast it for its prophecy cost as long as it's exiled.)

Whenever you activate an ability of a creature that isn't a mana ability, Moranai Tracker gets +1/+1 until end of turn.

Return up to two target creature cards from your graveyard to your hand.

{T}: Add {W}.
{W}, {T}: Target creature gains vigilance until end of turn.

When Morose Bohemian enters, scry 1, then draw a card.

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you cast a noncreature spell, each opponent loses life equal to Morose Harpist's power.

Target opponent mills five cards, then you exile up to two instant and/or sorcery cards from that player's graveyard. You may cast those cards for as long as they remain exiled, and you may spend mana as though it were mana of any type to cast them.

Choose one —
• Destroy target artifact or enchantment.
• Search your library for up to two basic land cards, reveal them, put them into your hand, then shuffle.

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.)

Mortalcoil Hydra enters with a number of +1/+1 counters on it equal to the amount of mana spent to cast it.
When Mortalcoil Hydra dies, each opponent loses 3 life and you gain 3 life.
Foreshadow {4}{B}{G} (You may cast this spell for its foreshadow cost. If you do, also trigger its “dies” abilities when it enters.)

Whenever Mortified Medium or another creature enters, you gain 1 life.
As long as you have at least 10 life more than your starting life total, Mortified Medium gets +4/+4 and has flying.