msem-instigator

Target opponent reveals their hand, exiles each nonland card from it, then conjures a card named Data-Point into their hand for each card exiled this way. (It's a sorcery that costs {2} with “Draw a card.”)

Enchant player
Whenever enchanted player casts a spell, they reveal cards from the top of their library until they reveal a card that shares a type with that spell, then puts all cards revealed this way into their graveyard.

When Memory Figment is put into your graveyard from your hand or library, you may exile it. If you do, for as long as it remains exiled, you may cast it. It costs {2} less to cast this way.

Whenever Memory of Fatalism dies or you cast a noncreature spell, each opponent loses 2 life and you gain 2 life.
{4}: Put Memory of Fatalism from your graveyard on top of your library.

Draw X cards and you gain X life, where X is the number of card types among permanents you control.

Chosen one ({W}{U}{B}{R}{G}: Transform this permanent.)
[+2]: Exile the top two cards of your library. Until end of turn, you may play one card exiled with this permanent.
[+1]: Exile up to two cards from your hand, then draw that many cards.
[–3]: Menna, Servant to None deals 3 damage to up to one target player and up to one target creature or planeswalker.

When Mental Supremacist enters, choose target creature you don't control. That creature has base power and toughness 1/1 and loses all abilities for as long as you control Mental Supremacist.

Menace

Menace (This creature can't be blocked except by two or more creatures.)
Whenever Mercenary Coercer deals combat damage to a player, that player discards a card.

Adorned — Mercenary Lancer gets +2/+2 as long as it's equipped and/or enchanted.

Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
{2}{B}, Discard a card: Mercenary of the Folded Fan gains indestructible until end of turn. Tap it. If you're in a renaissance, draw a card.

Whenever Merchant of Flesh or another creature you control dies, create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)
{B}, Sacrifice two Treasures: Each opponent sacrifices a creature.

Armed — Merciless Brute gets +2/+2 as long as it's equipped.

Whenever Merciless Shieldbreaker enters or attacks, target opponent puts three rust counters on a permanent they control with no rust counters on it. That permanent gains “At the beginning of your upkeep, remove a rust counter from this permanent. Then if there are no rust counters on this permanent, sacrifice it and it deals 4 damage to you.”

{2}{G/U}{G/U}, {T}: Untap each non-Lizard permanent you control.

{1}{U}: Mercurial Merfolk gets +2/-2 until end of turn.
When Mercurial Merfolk dies, draw a card.

Whenever Merfolk Visionary or another Merfolk creature you control enters, scry 2. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

Skip your draw step.
At the beginning of your upkeep, shuffle your hand and graveyard into your library, then draw three cards.
You can't cast more than one spell each turn.

Improve {1}{G/U} ({1}{G/U}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
You may play an additional land on each of your turns.
Wanderlust — At the beginning of your end step, if you control four or more differently named lands, you may draw a card.

Flying, haste
{X}{R}{R}, Exile an instant or sorcery card with mana value X from your graveyard: Return Merkurio's Familiar from your graveyard to the battlefield. It gets +X/+0 until end of turn.

I, II — Target creature you control gets +2/+0 and gains menace until end of turn.
Discovery — Attacking creatures you control get +2/+0 and have menace.

Whenever another artifact you control enters, put a +1/+1 counter on Metalwork Machinist.

Artifact spells you cast cost {1} less to cast.
{2}, Sacrifice an artifact: Target creature gains deathtouch until end of turn.

When Mettalia's Forward enters, you may salvage a card. (Exile one from your graveyard until this creature leaves the battlefield. Whenever this creature deals combat damage to a player, put a card it salvaged into your hand.)

Mettalia is all colors.
Mettalia has protection from each color among cards she's salvaged in exile.
When Mettalia enters, for each color, you may salvage a nonlegendary card of that color. (Exile one from your graveyard until this creature leaves the battlefield. Whenever this creature deals combat damage to a player, put a card it salvaged into your hand.)