msem-instigator

Swarm of Sporemites gets +1/+1 for each creature card and Revelation card in your graveyard.

Synchronous Battle Armor and equipped creature get +1/+1 for each artifact you control.
Whenever equipped creature attacks, tap up to three target creatures.
Reconfigure {3}{U}{U} ({3}{U}{U}: Attach to target creature you control; or unattach from a creature. Reconfigure only as a sorcery. While attached, this isn't a creature.)

Flying
Synchronous Hellkite enters with a +1/+1 counter for each other artifact you control.
Sacrifice three artifacts: Return Synchronous Hellkite from your graveyard to the battlefield.

TT-20 Salvation gets +1/+1 for each other artifact you control.
As TT-20 Salvation enters, create a 1/1 colorless Servo artifact creature token.

Tarmovore's power and toughness are each equal to twice the number of card types among cards in all graveyards.

Flying
Tawny Prophet enters with three +1/+1 counters on it.
{W/U}, Remove a +1/+1 counter from Tawny Prophet: Scry 1, then draw a card.

Enspirit (As you cast this spell, you may exile a nonenchantment creature you control until this leaves the battlefield or fails to resolve. Reduce this spell's cost by the exiled card's mana value.)
Tenacious Brawler enters with X +1/+1 counters on it.

Terra Novea's power and toughness are each equal to the number of permanents you control.
{T}: Add {G} for each land you control.

The Mythical Zhiwu enters with four +1/+1 counters on it.
{1}, Remove a +1/+1 counter from a creature you control: Target creature gets -1/-1 until end of turn. Activate only as a sorcery.
{1}, Remove a +1/+1 counter from a creature you control: Each opponent loses 1 life and you gain 1 life.

The Urchin King's power and toughness are each equal to the number of cards in all graveyards.
Sacrifice a creature: The Urchin King gains lifelink and indestructible until end of turn.

Flash
Thorn-Touch Abomination enters with X +1/+1 counters on it.

Trample, haste
Thriving Hydra enters with four +1/+1 counters on it.
When Thriving Hydra enters, for each other creature you control, put X +1/+1 counters on that creature, where X is four minus its power.
Whenever Thriving Hydra attacks, double the number of +1/+1 counters on each creature you control.

You may have Undecided Mimic enter or phase in as a copy of any creature on the battlefield, except it has this ability and “{2}{U}{U}: Undecided Mimic phases out.” (Treat it and anything attached to it as though they don't exist until its controller's next turn.)

Unearthed Legion's power and toughness are each equal to the number of cards in your graveyard.
At the beginning of your upkeep, mill a card.

Unending Slime enters with X +1/+1 counters on it.
{2}{G}{G}{G}: Return Unending Slime from your graveyard to your hand.

You may have Unstable Impersonator enter as a copy of any creature on the battlefield chosen at random.

You may have Urushi, the Ripple in the Smoke enter as a copy of any creature on the battlefield, except it's an enchantment. (It's not a creature.)

Vigorbreath Scourge enters with X +1/+1 counters on it.
Whenever Vigorbreath Scourge attacks, it gets +X/+X until end of turn, where X is your devotion to green. Then if its power is 6 or greater, draw a card. (Each {G} in the mana costs of permanents you control counts toward your devotion to green.)

Vitalhydra enters with twice X +1/+1 counters on it.
Each other creature you control enters with a number of additional +1/+1 counters on it equal to the number of +1/+1 counters on Vitalhydra.

Trample
Volcanic Terror gets +1/+1 for each land card in all graveyards and in exile.

WZ-18 Troublemaker enters with a +1/+1 counter on it.
When WZ-18 Troublemaker dies, put its counters on target creature you control.
{1}{R}, Exile WZ-18 Troublemaker from your graveyard: It deals 2 damage to each opponent.

Flying
Warden of Harshapal Tower's power and toughness are each equal to the number of creatures you control.

Warden of the Fronds' power and toughness are each equal to the number of Forests you control.
Warden of the Fronds has indestructible as long as you control five or more lands.

As Warmonger Contraption enters, choose a creature type.
Warmonger Contraption is the chosen type in addition to its other types.
Warmonger Contraption's power and toughness are each equal to the number of creatures of the chosen type you control.

You may have Warped Physiognomist enter as a copy of any creature on the battlefield with mana value 3 or less.