msem-instigator

When Astrid, Disgruntled Princess enters, destroy target creature with mana value less than or equal to the number of Warriors you control.

Whenever Highpeak Rider attacks, search your library for a land card and put it onto the battlefield, then shuffle. Sacrifice that land at the beginning of the next end step.

{T}: Add {C}.
{2}: Idravir becomes a 2/2 creature with undying in addition to its other types until end of turn. (When that creature dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)

({T}: Add {B}.)
Wretched Sanctuary enters tapped with two sanctum counters on it.
{T}, Remove a sanctum counter from Wretched Sanctuary: Add {U} or {R}.

Smelting Breath deals 5 damage to target creature. Destroy up to one Equipment attached to that creature.

Inscrutable Realms enters tapped unless you control two or more other lands.
{T}: Add {W}.
{T}, Pay 1 life: Add {G} or {U}.

When Hoof Cliff Caretaker enters, return target card of an opponent's choice from your graveyard to your hand.

When Kaneh Scribe enters, amass Soldiers 2. (Put two +1/+1 counters on an Army you control. It's also a Soldier. If you don't control one, create an 0/0 black Soldier Army creature token first.)

When Greypelt Clergy enters, choose one —
• Put a +1/+1 counter on Greypelt Clergy.
• Permutate. (You may remove a counter from a creature you control. If you do, put two +1/+1 counters on a different creature you control.)

As Destroyed Isle enters, you may pay 3 life. If you don't, it enters tapped.
{T}: Add {W}, {U}, or {B}.

You may look at the top card of your library any time.
You may play lands and cast spells from the top of your library.
As long as your main library has ten or fewer cards in it, you may cast spells without paying their mana costs.

Kaur, End of Lies costs {X} less to cast, where X is the greatest mana value among permanents your opponents control.
[+2]: Reveal the top card of your library. If it's a permanent card, put it onto the battlefield.
[–4]: Exile target noncreature permanent, then reveal the top four cards of your library. You may put a permanent card from among them onto the battlefield. Put the rest into your graveyard.
[–12]: Search your library for up to X permanent cards, where X is the number of permanents you control, put them onto the battlefield, then shuffle.

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
Lifelink

Alluring Rider must be blocked if able.
Attain {4}{G} ({4}{G}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

As an additional cost to cast this spell, sacrifice a land.
Creatures you control get +1/+1 and gain trample until end of turn for each land you control.

Menace
Whenever a creature an opponent controls dies, create an Idol token. (It's an artifact with “{1}, Sacrifice this artifact: Put a +1/+1 counter on target creature. Activate only as a sorcery.”)

Colossal 3—{6}{R} (You may cast this for its colossal cost to have it enter with three +1/+1 counters; or pay {6}{R} as a sorcery: Put three +1/+1 counters on it if it has none.)

Tap target creature. Prevent all damage that would be dealt to and dealt by that creature this turn.

You have hexproof.
Whenever you cast a noncreature spell, you may tap or untap target permanent.

Counter target spell unless its controller pays {3}. If you own a foretold card in exile, counter that spell unless its controller pays {6} instead.

Double strike
Motley — As long as there are five or more names among nonland permanents you control, Champion of Blades has vigilance, trample, and haste.

Guardian of Dusk gets +X/+X, where X is the amount of life you've lost this turn.
When Guardian of Dusk has power 13 or greater, sacrifice it. If you do, you gain life equal to its power.

Whenever you cast an instant or sorcery spell, you may attach Stormbreaker's Edge to target creature you control.
Equipped creature gets +3/+0.
Equip {3}

All creatures able to block Orphaned Nuckalavee do so.

First strike
Whenever this creature attacks, put a geode counter on target land you control. It gains “{1}, {T}, Sacrifice this land: Draw a card and you gain 2 life” for as long as it has a geode counter on it.