msem-instigator

When Screams from the Deep enters, exile up to one target monocolored permanent.
As long as an opponent owns three or more cards in exile, you may have Screams from the Deep assign its combat damage as though it weren't blocked.
Evoke {5} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

When Scribal Puppeteer enters, create two 1/1 black Puppet creature tokens with “At the beginning of your upkeep, you lose 1 life.”

Trample
When Sealer of Pacts enters, sacrifice any number of permanents, then draw that many cards.

First mate—Each nonland card in your starting deck targets or has an ability that targets. (If this card outside the game is your chosen first mate, you may swap it with a card in your opening hand.)
Hexproof
Whenever a permanent you don't control becomes the target of a spell or ability you control, create a token that's a copy of that permanent.

Seaside Skimmer can't be blocked if you've cast a Dragon spell or Adventure spell this turn.

Trample
Seasoned Adventurer enters with two +1/+1 counters if you control seven or more lands.

{T}, Sacrifice a creature: When you next cast an instant or sorcery spell this turn, copy that spell. You may choose new targets for the copy.

Breach (Whenever this deals combat damage to a player, you may have it become an Aura Curse until your next turn. Attach it to that player.)
Each cursed opponent must attack with at least one creature each combat if able.

When Seeker of Horizons enters, reveal the top three cards of your library. You may put a permanent card from among them into your hand. Put the rest on the bottom of your library in any order.
Recite {1}{U} (You may cast this creature from your graveyard for its recite cost. If you do, exile it when it enters or if it would leave the battlefield.)

Deathtouch
Cards can't leave graveyards.
If a creature would die, you may pay {X}, where X is the number of cards in your graveyard. If you do, instead exile it, then return that card to the battlefield under your control.

Concord — This spell costs {4} less to cast if there are four or more card types among permanents you control.
Vigilance, trample, lifelink, haste

At the beginning of your end step, for each opponent, destroy up to one target creature that player controls with power less than or equal to the amount of life that player lost this turn.
{3}{R}: Selezzar, Tyrant of Endak deals 2 damage to each opponent.

Flying, vigilance, lifelink
Persist (When this 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.)

This spell can't be countered.
Flying, protection from cryptic
Whenever you cast a cryptic spell, cast a Sphinx spell, or draw a card, investigate.
{T}, Sacrifice ten Clues: You win the game.

Flying
When Sha Long enters, each player chooses an artifact they control, then sacrifices the rest. If they don't control an artifact, they may return an artifact card from their graveyard to the battlefield. Repeat this process for creatures, enchantments, and planeswalkers.

{U}{R}{W}, Discard a card named Sha'Iv, God of Order: Sha'Iv gains indestructible and becomes a God creature in addition to its other types.
Whenever Sha'Iv enters or attacks, choose target creature an opponent controls. Untap it, then tap each other creature that player controls. They don't untap during their controller's next untap step.

Whenever Shah's Caravan attacks, creatures you control get +1/+1 until end of turn. If you control three or more Satrapies, creatures you control can't be blocked by creatures with power 2 or less this turn.
Satrapycycling {2} ({2}, Discard this card: Search your library for a Satrapy card, reveal it, put it into your hand, then shuffle.)

Haste
Whenever Shala's Phantasm attacks, you may sacrifice a creature. If you do, Shala's Phantasm deals 3 damage to any target.

Trample
Shapen, Spiteful Creation must be blocked each combat if able.
The first time Shapen, Spiteful Creation would be dealt damage each turn, prevent that damage.

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you cast a noncreature spell, 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.”)

When Shardsong Seedling enters, conjure two cards named Data-Point into your hand. (It's a sorcery that costs {2} with “Draw a card.”)

Vigilance
Whenever one or more creatures you control deals combat damage to a player, you may discard a card. If you do, create a Function token with “Draw two cards.” (It's an enchantment. As you cast an instant or sorcery spell, sacrifice any number of Functions to add their effects to that spell.)

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.)
Trample
{1}, Discard Shifting Brute: Add one mana of any color. Scry 1.

Flash
This spell can't be countered.
Whenever Shigurei attacks, you may activate an ability of a creature you control without paying its cost.
{1}{G}{U}: Target permanent becomes a colorless Island land until end of turn.

Trample
When Shigurei, the Floodbringer enters, up to three target permanents become colorless Island lands.