msem-instigator

Breach (Whenever this deals combat damage to a player, you may have it become an Aura Curse until your next turn. Attach it to that player.)
Recursive — As long as Mayar, Nullcrowned is a Curse, they have all nonrecursive abilities of other Curses and creatures with breach you control.
Pay 3 life: Target enchantment creature gains haste and menace until end of turn.

This spell can't be countered.
Flying, haste
Mayu, the Endless Flow gets +2/+2 for each spell you've cast this turn.

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.)

When Meadow Songstress enters, conjure three cards named Meadow Songstress and shuffle them into your main library.
Whenever a nontoken creature you control enters, if it shares a name with one or more other creatures you control, draw a card.

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.

Gain control of target creature with power X or less.

Meandering Path enters tapped unless you control one or fewer other lands.
{T}: Add {R} or {G}.
Cycling {2} ({2}, Discard this card: Draw a card.)

Shuffle the cards from your hand into your library, then draw that many cards.
Draw a card.

Enchant creature
You control enchanted creature.

Indestructible (Damage and effects that say “destroy” don't destroy this creature.)

When Mechanical Mastodon enters, you may return another target permanent you control to its owner's hand.

Deploy 4 (As this enters, you may tap any number of other creatures you control with total power 4 or more.)
When Mechanical Tactician enters deployed, tap up to two target creatures an opponent controls. Those creatures don't untap during their controller's next untap step.

Mechanized Ideal gets +X/+Y, where X is the highest base power among other creatures you control and Y is the highest base toughness among other creatures you control.

Flying
{2/B}{2/B}, {T}, Sacrifice Meddling Gargoyle: Target opponent reveals their hand. You choose a nonland card from it. That player discards that card. Activate only as a sorcery.

When Medical Mask enters, prevent the next 3 damage that would be dealt to any target this turn.
{4}, Sacrifice Medical Mask: Prevent the next 6 damage that would be dealt to any target this turn.

I, II — Put a +1/+1 counter on target creature you control.
Discovery — Creatures you control with +1/+1 counters on them have lifelink.

Equipped creature gets +1/+1.
Whenever equipped creature becomes the target of a spell, you gain 3 life.
Equip {4}

Trample
Enchantment spells and Aurashaper spells you cast cost {1} less to cast.
Whenever another enchantment you control enters, draw a card.

At the beginning of combat on your turn, if you cast an enchantment spell, an instant spell, and a sorcery spell this turn, create two 3/3 red Shark enchantment creature tokens. You may have any number of those tokens gain haste. If you do, sacrifice the tokens you chose at end of combat.

Lifelink, menace

Whenever a player discards a card, you may draw a card and put a loyalty counter on Mei Liva, the Broken.
[0]: Target permanent's controller sacrifices it unless they discard two cards.
[–1]: Each opponent loses X life and you gain X life, where X is the number of cards in your hand.
[–3]: Target player chooses a card in their hand, then discards the rest.

[+1]: Search each player's graveyard, hand, and library for any number of cards with the same name as target nonbasic card in a graveyard and exile them. Then each player shuffles.
[–2]: Each player draws two cards, then each opponent exiles two cards at random from their hand.
[–5]: You may cast a card exiled with Mei Liva without paying its mana cost.

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Whenever a marked creature dies, put a +1/+1 counter on Mei's Collector.

Whenever Mei's Student deals combat damage to a player, fateseal 1, then scry 1. (Look at the top card of an opponent's library, then you may put it on the bottom.)

Flying
When Mei's Understudy enters, if you control another Actor, draw a card.