msem-instigator

(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, create a 0/2 white Ox creature token.
A creature you control dies.
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.)

Nightshaper's Domain enters tapped.
{T}: Add {B}.

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.

Whenever a land you control enters, put a +1/+1 counter on Nimble Pathfinder.
Surpass {5}{G} ({5}{G}: Transform this creature. This costs {1} less to activate for each counter on it. Activate only as a sorcery.)

Nimblefoot can't be blocked.

When Ninhasir's March enters, 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.

Target creature you control gains haste until end of turn. Return it to its owner's hand at the beginning of the next end step.

Whenever Ontarachie Hunter attacks, each opponent loses 1 life.
At the beginning of your end step, if an opponent has 10 or less life, transform Ontarachie Hunter.

Whenever Optimistic Chronicler deals damage to a player or noncreature permanent, surveil 1, then draw a card.

Whenever Orphan Prodigy is dealt damage, it deals that much damage to target player.
Attain {4}{R} ({4}{R}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

All creatures able to block Orphaned Nuckalavee do so.

Out-of-Depth Amateur can't attack or block alone.
Attain {4}{R} ({4}{R}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

Whenever Overgrowth Host attacks, germinate. Then creatures you control that are Saprolings or have counters on them gain trample until end of turn.
Saprolings you control get +1/+1.

Whenever you sacrifice a permanent, Overseer of Armies deals 1 damage to each opponent and each battle they protect.

(Transform this if it's not attached to a creature. Pay {G} as a sorcery to unattach it.)
Enchant creature you control
When this permanent transforms into Packbond Mount, move all +1/+1 counters from it to its rider.
Packbond Mount's rider gets +1/+1.
{2}{G}: Put a +1/+1 counter on Packbond Mount's rider.

Whenever a creature dies, Pakka, the Shadowcloak deals 1 damage to each opponent.