Flying

Whenever a nontoken creature you control dies, investigate.

Clues you control have exalted. (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn for each instance of exalted among permanents you control.)

Merchant Ship can't attack unless defending player controls an Island.

Whenever Merchant Ship attacks and isn't blocked, you gain 2 life.

When you control no Islands, sacrifice Merchant Ship.

Afflict 2 (Whenever this creature becomes blocked, defending player loses 2 life.)

, Discard a card: Merciless Eternal gets +2/+2 until end of turn.

Freerunning (You may cast this spell for its freerunning cost if you dealt combat damage to a player this turn with an Assassin or commander.)

When Merciless Harlequin enters, you draw a card and you lose 1 life.

At the beginning of each upkeep, if a player cast two or more spells last turn, transform Merciless Predator.

Flying

Whenever you cast an instant or sorcery spell, Mercurial Geists gets +3/+0 until end of turn.

You may have Mercurial Pretender enter as a copy of a creature you control, except it has ": Return this creature to its owner's hand."

Outlast (, : Put a +1/+1 counter on this creature. Outlast only as a sorcery.)

Each creature you control with a +1/+1 counter on it has deathtouch.

: Destroy target creature with islandwalk.

Whenever a creature you control explores, Merfolk Cave-Diver gets +1/+0 until end of turn and can't be blocked this turn.

Flying

Whenever you cast a kicked spell, scry 2.

, : Target player mills two cards.

When Merfolk Observer enters, look at the top card of target player's library.

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

Phasing (This phases in or out before you untap during each of your untap steps. While it's phased out, it's treated as though it doesn't exist.)

Flying

When Merfolk Skydiver enters, put a +1/+1 counter on target creature you control.

: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Other Merfolk creatures you control get +1/+1.

: Target Merfolk creature can't be blocked this turn.

: Switch target creature's power and toughness until end of turn.

Flash

When Merfolk Trickster enters, tap target creature an opponent controls. It loses all abilities until end of turn.

Flying

Whenever Merfolk Windrobber deals combat damage to a player, that player mills a card. (They put the top card of their library into their graveyard.)

Sacrifice Merfolk Windrobber: Draw a card. Activate only if an opponent has eight or more cards in their graveyard.

Whenever one or more Halflings you control attack a player, create a Food token. (It's an artifact with ", , Sacrifice this artifact: You gain 3 life.")

Merieke Ri Berit doesn't untap during your untap step.

: Gain control of target creature for as long as you control Merieke Ri Berit. When Merieke Ri Berit leaves the battlefield or becomes untapped, destroy that creature. It can't be regenerated.

, : Target creature gets -2/-0 until end of turn. ( is the untap symbol.)

: Target creature gains flying until end of turn.

Whenever you cast a blue spell, you may untap Merrow Levitator.

, : Merrow Wavebreakers gains flying until end of turn. ( is the untap symbol.)

When Merry Bards enters, you may pay . When you do, create a Young Hero Role token attached to target creature you control. (If you control another Role on it, put that one into the graveyard. Enchanted creature has "Whenever this creature attacks, if its toughness is 3 or less, put a +1/+1 counter on it.")

Partner with Pippin, Warden of Isengard (When this creature enters, target player may put Pippin into their hand from their library, then shuffle.)

Whenever one or more artifacts you control enter, create a 1/1 white Soldier creature token with lifelink. This ability triggers only once each turn.

Stand up, Flap your arms, Cluck like a chicken: Mesa Chicken gains flying until end of turn.

Flying

: Mesa Falcon gets +0/+1 until end of turn.

Flying; banding (Any creatures with banding, and up to one without, can attack in a band. Bands are blocked as a group. If any creatures with banding you control are blocking or being blocked by a creature, you divide that creature's combat damage, not its controller, among any of the creatures it's being blocked by or is blocking.)

When Mesmeric Fiend enters, target opponent reveals their hand and you choose a nonland card from it. Exile that card.

When Mesmeric Fiend leaves the battlefield, return the exiled card to its owner's hand.

All Slivers have "When this permanent enters, you may fateseal 1." (To fateseal 1, its controller looks at the top card of an opponent's library, then they may put that card on the bottom of that library.)

Flying

When Messenger Drake dies, draw a card.

Flying

Council's dilemma — When Messenger Jays enters, starting with you, each player votes for feather or quill. Put a +1/+1 counter on Messenger Jays for each feather vote and draw a card for each quill vote. For each card drawn this way, discard a card.

As Metallic Mimic enters, choose a creature type.

Metallic Mimic is the chosen type in addition to its other types.

Each other creature you control of the chosen type enters with an additional +1/+1 counter on it.

, : Regenerate target artifact.

: Reveal any number of artifact cards in your hand. Add for each card revealed this way.

Lifelink

When Metamorphosis Fanatic enters, return up to one target creature card from your graveyard to the battlefield with a lifelink counter on it.

Miracle (You may cast this card for its miracle cost when you draw it if it's the first card you drew this turn.)

Flying

: You may put a creature card with mana value X from your hand onto the battlefield. If you do, return Metathran Aerostat to its owner's hand.

Metathran Soldier can't be blocked.

: Regenerate Metathran Zombie.

Flying

Whenever you attack with one or more creatures with counters on them, draw a card.

Flying

: Metropolis Sprite gets +1/-1 until end of turn.

Whenever Miara, Thorn of the Glade or another Elf you control dies, you may pay and 1 life. If you do, draw a card.

Partner (You can have two commanders if both have partner.)

When Miasmic Mummy enters, each player discards a card.

When Michonne enters, create two Walker tokens.

As long as Michonne is equipped, she must be blocked if able.

Whenever Michonne and at least two Zombies attack, she gains indestructible until end of turn.

When Midnight Arsonist enters, destroy up to X target artifacts without mana abilities, where X is the number of Vampires you control.

Wither (This deals damage to creatures in the form of -1/-1 counters.)

At the beginning of your upkeep, put a -1/-1 counter on each nonblack creature.

Other Aetherborn you control get +1/+1.

Whenever Midnight Entourage or another Aetherborn you control dies, you draw a card and you lose 1 life.