msem-instigator

Gruff Clutch enters with six +1/+1 counters on it.
{R}, Remove a +1/+1 counter from Gruff Clutch: It deals 1 damage to any target.

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.

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

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.

Augury Hydra enters with X +1/+1 counters on it.
When Augury Hydra enters, scry Y, where Y is its power, then draw Y cards.

Trample
Avatar of the Groves enters with a +1/+1 counter on it for each land you control.
Landfall — Whenever a land you control enters, proliferate. (Choose any number of permanents and/or players with counters on them, then give each another counter of each kind already there.)

Search your library for a land card, put it onto the battlefield tapped, then shuffle.
Coalesce {5}{G}{G} (You may cast this from your graveyard for {5}{G}{G}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)
Beyond All Horizons's power and toughness are each equal to the number of lands you
control.

Trample
Colossal Greatwurm enters with five +1/+1 counters on it.
Whenever a player draws a card, put a +1/+1 counter on Colossal Greatwurm.
Remove three +1/+1 counters from Colossal Greatwurm: Create a 3/3 green Wurm creature token.

Tithe (As you cast this spell, you may tap three artifacts and/or creatures you control.)
Croakfolk Marsh-Baron enters with X +1/+1 counters on it. If its tithe was paid, it enters with twice X +1/+1 counters instead.

Hexproof
Crossworld Wanderer gets +1/+1 for each differently named land you control.

Spirited (When this creature enters, you may activate one of its activated abilities without paying its cost.)
Dragonmaw Wurm enters with X +1/+1 counters on it.
{1}{G}, {T}: Target creature you control fights another target creature.

Elemental Envelopment enters with X +1/+1 counters on it.
When Elemental Envelopment enters, if you controlled a green legendary creature or planeswalker as you cast it, search your library for any number of Elemental creature cards with total mana value X or less, where X is Elemental Envelopment's power, put them onto the battlefield, then shuffle.

Eternal Oak gets +1/+1 for each creature you control.
Whenever a nontoken creature you control dies, create a 1/1 green Saproling creature token.

Trample
Evergrowing Hydra enters with X +1/+1 counters on it.
Whenever another creature you control dies, you may pay {X}, where X is less than or equal to that creature's power. If you do, put X +1/+1 counters on Evergrowing Hydra.

Fardancer Liege's power and toughness are each equal to the number of colors of mana that lands you control could produce.

Forestheart Elemental enters with a +1/+1 counter on it for each land you control.

Frilled Hydra enters with X +1/+1 counters on it.
Defiance (Whenever this creature takes damage, if it survives and wasn't defiant, put a +1/+1 counter on it and it becomes defiant.)
Frilled Hydra has hexproof as long as it's defiant.

Trample
Gloamrazer Hydra enters with four +1/+1 counters on it.
Whenever a nontoken creature you control dies, if it was embattled, create an X/X green Hydra creature token, where X is that creature's power. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

Archive 6
Grohl's Study's power and toughness are each equal to the number of cards in the archived library.
Whenever Grohl's Study deals combat damage to a player, you may put a card from the archived library into your hand.

Horizon Wayfarer's power and toughness are each equal to the number of differently named lands you control.

(Transcend as a sorcery to gain that type and a +1/+1 counter.)
Jutou enters with X +1/+1 counters on her.
{3}{G}: Demigod — You gain life equal to the greatest power among creatures you control.
{6}{G}: God — Search your library for a creature card with the same power as a creature you control, put it onto the battlefield, then shuffle.

Mistwake Hydra enters with X +1/+1 counters on it.
Creatures with power less than Mistwake Hydra's power can't block it.

Okrophore's power and toughness are each equal to the number of colorless cards in your graveyard.

Pelagic Hydra enters with seven +1/+1 counters on it.
{1}{G}: Put a +1/+1 counter on Pelagic Hydra.
Remove a +1/+1 counter from Pelagic Hydra: It deals 1 damage to target creature blocking or blocked by it.

Trample
Qiyan enters with twice X +1/+1 counters on them.
If damage would be dealt to Qiyan while they have a +1/+1 counter on them, prevent that damage, remove that many +1/+1 counters from Qiyan, then create a 0/0 green Hydra creature token and put twice that many +1/+1 counters on it.