msem-instigator

{1}{G}: Create a 1/1 colorless Construct artifact creature token.
{2}{G}{G}: Target creature you control becomes 4/4. (This lasts indefinitely.)
{4}{G}{G}{G}{G}: Put four +1/+1 counters on each creature you control with power 4 or greater.

Destroy target artifact, enchantment, or planeswalker.
Reconstruct {4}{G}{G} (You may cast this from your graveyard for its reconstruct cost reduced by the mana value of a permanent you sacrifice as you cast it this way. Then exile this.)

Flying, trample
Once during each of your turns, you may cast a spell from your graveyard without paying its mana cost.
When Yhzag, Alpha and Omega is put into a graveyard from anywhere, its owner shuffles their graveyard into their library.

Yi Cang, Thief of Blessings enters with a +1/+1 counter on them.
{1}: Yi Cang becomes a copy of target creature in their pack, except their name is Yi Cang, Thief of Blessings, they're legendary in addition to their other types, and they have this ability. (Two or more creatures you control with equal power are in a pack.)

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.

Choose three. You may choose the same mode more than once.
• Put a +1/+1 counter on up to one target creature you control, then you may have it fight target creature you don't control.
• Target player creates a 2/2 green Lizard creature token.
• You mill four cards and gain 4 life.

Vigilance
{X}{G}, {T}: Ylda, the Wild Soul becomes a copy of target creature you control with mana value X, except it has this ability and vigilance. Activate only as a sorcery.

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.

Reach
Renown 1 (When this creature deals combat damage to a player, if it isn't renowned, put a +1/+1 counter on it and it becomes renowned.)

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.)

{T}, Pay 1 life: Add one mana of any color.

Flying
First strike (This creature deals combat damage before creatures without first strike.)
Lifelink (Damage dealt by this creature also causes you to gain that much life.)

Flying (This creature can't be blocked except by creatures with flying or reach.)
When Young Tempter enters, you draw a card and you lose 1 life.

Double strike, haste

Target creature gains haste and trample until end of turn.
Fabled {3}{R/G}{R/G} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that creature.)

Soldiercycling {2}{W} ({2}{W}, Discard this card: Search your library for a Soldier card, reveal it, and put it into your hand, then shuffle.)

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

You have hexproof.
Adorned — Youthful Savior has hexproof as long as it's equipped and/or enchanted.

Whenever you draw your second card each turn, put a +1/+1 counter on Youthful Tortoise.
Cycling {2} ({2}, Discard this card: Draw a card.)

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.