msem-instigator

Whenever another nontoken creature you control enters, create a 1/1 green Saproling creature token.
{1}{G}, {T}: Populate. (Create a token that's a copy of a creature token you control.)

Exile target blocking or blocked creature. If that creature had a +1/+1 counter on it, you gain life equal to its power.

Reach, trample
When Anran, Root Steward enters, destroy up to three target noncreature permanents. For each permanent destroyed this way, its controller creates a colorless enchantment land token named Paradise with hexproof and “{T}: Add one mana of any color.”

You may put a creature or Revelation card from your hand onto the battlefield. Exile that permanent if it would leave the battlefield. If it's a Revelation, it enters as a Horror creature.
Coalesce {7}{U}{U} (You may cast this from your graveyard for {7}{U}{U}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)

This spell costs {1} less to cast for each storied permanent you control. (Enchantments and legendary permanents are storied.)
Counter target spell.
Draw a card.

Creatures you don't control get -1/-1.
Mirage {1}{B} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)

Vigilance, trample
Whenever another Horror you control enters, choose one —
• Destroy target artifact or enchantment.
• You gain 4 life.
• Apex Abomination fights another target creature.

At the beginning of your upkeep, if an opponent controls more creatures than you, you may reveal the top seven cards of your library. Target opponent chooses a creature card revealed this way. Put that card onto the battlefield, and the rest into your graveyard.

Create an 8/8 blue Kraken creature token with hexproof.
Rerun (If you cast this from your hand, exile it as it resolves. Whenever a creature you control dies, you may cast this card from exile without paying its mana cost.)

At the beginning of your upkeep, if you control ten or more storied permanents, you win the game. (Enchantments and legendary permanents are storied.)

When Apprentice Summoner enters, search your library for a creature card with mana value 1 or less, put it onto the battlefield, then shuffle.

Enchant artifact or creature
At the beginning of each upkeep, if enchanted permanent is tapped, untap it.
You control enchanted permanent.

Counter target spell. Draw a card, then discard a card.

Flying, lifelink
Improve {1}{W/B} ({1}{W/B}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
Once each turn, when you gain life, you may have each opponent lose 2 life.

Flying
When Arbiter of Silence enters, exile all other creatures until Arbiter of Silence leaves the battlefield. (They return to the battlefield under their owners' control.)

Flash
Flying
As long as an opponent controls more creatures than you, Arbiter of the Scales gets +2/+2 and has first strike and lifelink.

This spell costs {1} less to cast for each differently named land you control.
Reach, trample

Trample
When Arborback Stomper enters, you gain 5 life.

Counter target spell. If a permanent spell is countered this way, create a Gold token. (It's an artifact with “Sacrifice this artifact: Add one mana of any color.”)

Prowess
When Arcane Dredger enters, return target instant or sorcery card from your graveyard to your hand.

Whenever Arcane Metalcrafter or another Wizard you control attacks, create a 1/1 colorless Construct artifact creature token that's tapped and attacking.
Whenever a Construct you control dies, Arcane Metalcrafter deals 1 damage to each opponent.

Counter target spell. If that spell is countered this way, until the end of your next turn the next spell you cast that shares a type with it costs {X} less to cast, where X is the countered spell's mana value.

When Arcanomancer enters, return up to one target instant card and up to one target sorcery card from your graveyard to your hand.

Flying
When Arcanum Owl enters, you may return target instant or sorcery card from your graveyard to your hand.

When Archaeomancer enters, return target instant or sorcery card from your graveyard to your hand.