msem-instigator

Whenever you sacrifice a permanent, you may put a -1/-1 counter on target creature.

(Transform this if it's not attached to a creature. Pay {1}{W} as a sorcery to unattach it.)
Enchant creature you control
Mount of Heroes's rider gets +2/+1.
Sacrifice Mount of Heroes: Counter target spell that targets you or Mount of Heroes's rider.

Whenever a land you control enters, put a +1/+1 counter on Mountain Runt, then it deals 1 damage to up to one target creature you don't control.
When Mountain Runt has three or more +1/+1 counters on it, remove them all and transform it.

Menace
At the beginning of your end step, Mountain Tyrant deals 1 damage to each creature you don't control.

At the beginning of combat on your turn, put a +1/+1 counter on target creature you control. If that creature has flying, transform Mounting Up.

Return target nonland permanent card with mana value 2 or less from your graveyard to the battlefield.
Acquiesce (If you cast this spell from your hand, exile it as it resolves. When one or more creatures you control deal combat damage to an opponent, you may cast this card from exile without paying its mana cost.)

Players can't get counters.
Counters can't be put on permanents.

When Mouthpiece of Yhzag enters, you may have target opponent create a tapped 1/1 colorless Human creature token.
Whenever Mouthpiece of Yhzag attacks, gain control of target Human creature you don't control with mana value 3 or less until end of turn. Tap it. It's attacking.

Whenever you tap a land for mana, add one mana of any type that land produced.
Whenever you cast a spell with mana value greater than the number of lands you control, sacrifice a land.

Sacrifice a creature or discard a card: Exile the top card of target player's library. You may cast that card for as long as it remains exiled. Any player may activate this ability but only once each turn and only during their turn.
You and permanents you control have hexproof from spells that were exiled with Mr. Jackston or that share a name with a card exiled with Mr. Jackston.

Deception {U}{B} ({U}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Ms. Moxie deals combat damage to a player, you may exile target nonland card with mana value 2 or less from your graveyard. If you do, cast a copy of that card without paying its mana cost.

Haste
Whenever Mukal Charger attacks during your first combat phase each turn, untap all Constructs you control. After this phase, there's an additional main phase followed by an additional combat phase.
Respawn (When this creature dies, if it attacked this turn, return it to its owner's hand.)

Trample, haste
Respawn (When this creature dies, if it attacked this turn, return it to its owner's hand.)
At the beginning of your end step, sacrifice a creature.

Exile a nonland card from your graveyard: For each colored mana symbol in that card's mana cost, add one mana of that color. Activate only once each turn. (For example, if the card's mana cost is {3}{G}{G}{W}, you add {G}{G}{W}.)

Look at the top three cards of your library, then put them into your graveyard or back on top of your library in any order.
Draw two cards.

Whenever a nontoken creature you control enters, if it shares no creature types with other creatures you control, draw a card.

Destroy target planeswalker. Mummy's Grin deals 2 damage to that planeswalker's controller.

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

{T}, Pay 1 life: Add {B}.
{T}, Pay 1 life, Sacrifice Murky Peat: Search your library for a Swamp card, put it onto the battlefield tapped, then shuffle.

({T}: Add {U} or {B}.)
Whenever Murmuring Falls becomes tapped, you lose 1 life unless you control two or more basic lands.

Untap all creatures that attacked this turn. After this main phase, there is an additional combat phase followed by an additional main phase. For each planeswalker you control, you may activate its loyalty abilities an additional time this turn.

At the beginning of your upkeep, germinate. Then if creatures you control have total power 10 or greater, transform Mushroom Merchant. (To germinate, put a +1/+1 counter on a creature or create a 1/1 green Saproling creature token.)

Counter target enchantment, instant, or sorcery spell. (Then exile this card. You may cast the creature later from exile.)

Put a +1/+1 counter on up to one target creature. (Then exile this card. You may play the land later from exile.)