msem-instigator

When Woopip Bruiser enters, germinate. When you do, you may have target non-Fungus creature get -X/-X until end of turn, where X is the greatest power among creatures you control. (To germinate, put a +1/+1 counter on a creature or create a 1/1 green Saproling creature token.)

When Woopip Sproutling enters, germinate. (Put a +1/+1 counter on a creature or create a 1/1 green Saproling creature token.)

Whenever an artifact you control enters or is put into a graveyard from the battlefield, Workshop Engineer gets +1/+1 until end of turn.

{T}, Sacrifice Worldshaper Adept: Choose two basic land types. Create a tapped colorless land token of the chosen types.

Flash
When Wormwood's Agent dies, create a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)

Each opponent sacrifices an artifact.
Scry 1.
Coalesce {6}{R} (You may cast this from your graveyard for {6}{R}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)

Haste
When Wretched Merfolk enters, target creature can't block this turn.

Trample
{2}{G}{U}: Look at the top two cards of your library. Put one of them into your hand and the other into your graveyard.

When Wu, the Shackled enters, you may have an opponent gain control of it. If you do, draw two cards.
At the beginning of your upkeep, if you don't own Wu, it fights another target creature you control and its owner draws a card.

Spirited (When this creature enters, you may activate one of its activated abilities without paying its cost.)
{4}{G}: Target creature gets +2/+2 until end of turn.

When Yamisaran Bladedancer enters, you may attach an Equipment you control to target creature you control.

Reach
{T}: Yangzhi Cloudpiercer deals 1 damage to target player or planeswalker.

Menace
Yaran's Enforcer gets +1/+1 as long as you foretold a card this turn.
Yaran's Enforcer gets +1/+1 as long as you cast a foretold spell this turn.

{2}, Exile a land card from your graveyard: Create a token that's a copy of that land.

Flying
When Yielder of Ambition enters, target creature gets +2/+2 until end of turn.
Fleeting {W} (You may cast this spell for its fleeting cost. If you do, sacrifice it at the beginning of the next end step.)

Whenever you cast a spell, harmonize twice. (To harmonize, trigger up to one harmony of a permanent you control.)
Harmony — Yita, Almgrove Prodigy gains your choice of flying, first strike, vigilance, lifelink, hexproof, or haste until end of turn.

When Young Chasqui enters, if you cast it, reveal the top five cards of your library. Put any number of creatures named Young Chasqui from among them into your hand. Put the rest of the revealed cards on the bottom of your library in a random order.
A deck can have any number of cards named Young Chasqui.

Young Dragonheart gets +1/+0 and has first strike as long as you control a legendary creature.

Wanderlust — Whenever a land you control enters, if you control four or more differently named lands, create a 1/1 green Saproling creature token.

Whenever you cast an instant or sorcery spell, tap target creature an opponent controls.

Whenever a nontoken creature you control dies, create a 1/1 black Skeleton creature token.

Whenever you cast a cryptic spell, create a 1/1 white Human creature token with lifelink. (Artifacts, enchantments, and modal spells are cryptic.)

Other Rebel creatures you control get +1/+0.
When Youthful Renegade enters, create a 1/1 white Rebel creature token.

Whenever Yri, the Daring Blade and exactly one other creature attack, Yri and that creature can't be blocked by creatures with mana value 3 or less this turn.

Vigilance
Art of war — At the beginning of your end step, if Yuso, Light of Jidai dealt damage to an opponent this turn, you may search your library for a creature card with mana value 2 or less, reveal it, put it into your hand, then shuffle.