msem-instigator

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Whenever Mistress of Frost extorts a spell, you may tap target artifact or creature.

Prowess, trample
When this creature transforms into Mortal Frame, add {R}{R}{R}.

{B}{G}{U}: Mother Roo gets +2/+2 and gains flying until end of turn.

Experience (Whenever this creature attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)

(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.

(Transform this if it's not attached to a creature. Pay {3}{R}{R} as a sorcery to unattach it.)
Enchant creature you control
Mount of the Order's rider gets +5/+4.
{2}{R}: Target creature can't block Mount of the Order's rider this turn.

Whenever a land enters the battlefield under your control, 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.

First strike
Whenever a creature dealt damage by Mournful Newborn this turn dies, transform Mournful Newborn.

Double strike

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.

(As you complete a condition, decode it. After all are decoded, you solve the mystery and transform it.)
When Mystery of the Crashed Craft enters the battlefield, create a 1/1 red Alien creature token.
{MG}—You cast an instant spell.
{MG}—You cast a sorcery spell.

(As you complete a condition, decode it. After all are decoded, you solve the mystery and transform it.)
When Mystery of the Dying Herds enters the battlefield, create a 0/2 white Ox creature token.
I — A creature you control dies.
II — You have 4 or more life than your starting life total.

Create a 1/1 white and black Badger Cleric creature token with lifelink. (Then exile this card. You may cast the creature later from exile.)

Flying
At the beginning of your upkeep, mill seven cards, then you may cast an instant or sorcery card from your graveyard. If that spell would be put into your graveyard, exile it instead.
If you would draw a card while your library has no cards in it, you win the game instead.

Nimblefoot can't be blocked.

When Ninhasir's March enters the battlefield, it deals 3 damage to any target.
{1}{R}{R}: Transform Ninhasir's March. Activate only if your fealty to Mountains is five or greater.

Indestructible
When this creature transforms into Ninhasir, God of Creation, discard all the cards in your hand, then draw that many cards plus one.
Whenever you cast an instant or sorcery spell, copy it. You may choose new targets for the copy.

Whenever No-Good Gunpointer attacks, you may pay 3 life. If you do, draw a card.

Trample
Ride {3}{G} ({3}{G}: Transform this and attach it to target creature you control without a Steed. Ride only as a sorcery.)

Flying

Tap target creature. That creature doesn't untap during its controller's next untap step.

Target attacking creature gets +3/+1 and gains trample until end of turn. (Then exile this card. You may cast the creature later from exile.)

Ominous Dragoncaller gets +1/+1 and has flying as long as you control a Dragon.