msem-instigator

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.

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

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.

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 Wayward Wanderers enters, you may have it become X/X with ward {X} and “Other creatures you control have base power and toughness X/X.”
{1}{G}: Return Wayward Wanderers to its owner's hand.

You may cast What Remains of Samuel Quinn from your graveyard and from the battlefield. It costs {G}{G} more to cast this way.
What Remains of Samuel Quinn enters with your choice of X counters from among +1/+1, vigilance, reach, and trample.

Trample
World Tender's power and toughness are each equal to twice the number of differently named lands you control.

You may have Better Half enter as a copy of any creature on the battlefield, except it's a Reflection in addition to its other creature types and it has distorted. (It can be blocked by tapped creatures but not untapped creatures.)

Flying, ward {2}
Intisuyu's Masterpiece gets +X/+X, where X is the number of artifacts and/or enchantments you control.

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.

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.)

You may have Graveborn Usurper enter as a copy of any creature card in a graveyard, except it has “{2}{U}{B}, Exile a creature card from a graveyard: Graveborn Usurper becomes a copy of the exiled card, except it has this ability.”

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.

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

Trample
Lumbering Ox gets +1/+1 for each land you control.
At the beginning of your upkeep, reveal the top card of your library. If it's a land card, you may exile it and repeat this process.
You may play cards exiled with Lumbering Ox.

Trample
Rubble Tender's power and toughness are each equal to the number of land cards in your graveyard.
At the beginning of your upkeep, sacrifice a land, then search your library for up to two land cards, put them onto the battlefield tapped, then shuffle.

Flying
Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
Angel of the Flock's power and toughness are each equal to the number of creatures you control.

Lifelink, trample
Champion of Stilthorpe's power and toughness are each equal to the number of Citizens and/or Peasants you control.

Garden Cherub's power and toughness are each equal to the number of creatures you control.
Garden Cherub can't be blocked by creatures with power 2 or less.

Protection from mana values lower than Ironwood Elemental's power (This permanent can't be blocked, targeted, dealt damage, or enchanted by anything with mana value lower than this creature's power.)
Ironwood Elemental's power and toughness are each equal to the number of creatures you control.

When Kahroba General enters, recruit. (Create a 0/0 white Soldier Army creature token, then put a +1/+1 counter on each Army you control.)
Kahroba General gets +1/+1 for each creature you control.

Archive 5 (As this enters, shuffle the top five cards of your main library into a new face up library. Sacrifice this after the archived library is empty.)
Encylopetia's power and toughness are each equal to the number of cards in the archived library.
At the beginning of your upkeep, exile a card from the archived library at random. You may play it this turn.

You may have Enthusiastic Double enter as a copy of any permanent on the battlefield, except it's 4/4, it's a creature in addition to its other types, and it has haste.