msem-instigator

Flying
Whenever you cast an artifact or enchantment spell, tap target artifact or creature an opponent controls. It doesn't untap during its controller's next untap step.

As long as you control exactly two creatures, those creatures get +2/+1 and have lifelink.

Schoolmaster gets +1/+1 for each other Merfolk you control.
When Schoolmaster enters, create a 1/1 white Merfolk creature token.

As Scion of Silence enters, choose a nonland card name.
Other permanents with the chosen name lose all abilities.

Menace (This creature can't be blocked except by two or more creatures.)
Whenever another creature dies, you may salvage a creature card. (Exile one from your graveyard until this creature leaves the battlefield. Whenever this creature deals combat damage to a player, put a card it salvaged into your hand.)

Concord — {1}{G}: Until end of turn, Seadrake Rider gets +2/+3 and must be blocked if able. Activate only during your turn, only once each turn, and only if there are four or more card types among permanents you control.

When Seafloor Cache enters and when you sacrifice it, create a Treasure token.
{1}{R}, Sacrifice Seafloor Cache: Draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

When Seafloor Casket enters and when you sacrifice it, target player mills two cards.
{1}{U}, Sacrifice Seafloor Casket: Draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

When Seafloor Shrine enters and when you sacrifice it, create a 1/1 white Merfolk creature token.
{1}{W}, Sacrifice Seafloor Shrine: Draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

When Seafloor Tomb enters and when you sacrifice it, exile up to two target cards from graveyards.
{1}{B}, Sacrifice Seafloor Tomb: Draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

When Seafloor Wreckage enters and when you sacrifice it, search your library for a basic land card, reveal it, put it into your hand, then shuffle.
{1}{G}, Sacrifice Seafloor Wreckage: Draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

Seafoam Slasher gets +1/+1 and has deathtouch as long seven or more cards are in your graveyard.
Cycling {2} ({2}, Discard this card: Draw a card.)

{T}: Add one mana of any color.
{2}, {T}: Draw a card. Activate only if you sacrificed a permanent or discarded a card this turn.

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.

Whenever Seasoned Lookout deals combat damage to a player, it voyages. (If it isn't blocking or targeted by another spell or ability, it phases out.)
Whenever Seasoned Lookout phases in, reveal the top card of your library. If it's a land card, put it onto the battlefield. Otherwise, put it into your hand.

Vigilance
Seawise Swain gets +1/+1 as long as you control an artifact.
Seawise Swain gets +1/+1 as long as you control an enchantment.

As an additional cost to cast this spell, sacrifice a creature.
Search your library for a creature card that shares a creature type with the sacrificed creature with mana value less than or equal to X plus the sacrificed creature's mana value, put it onto the battlefield, then shuffle.

When Sending Stones enters, harmonize twice. (To harmonize, trigger up to one harmony of a permanent you control.)
If you would harmonize, you may trigger a harmony of a permanent card in your graveyard instead.

Flying
Whenever you cycle Seraph of the Stage or it attacks, audition for white. (Create a 1/1 Construct Actor creature token, a Scout Role giving 2/3 and vigilance, or a Cleric Role giving 2/2 and lifelink. Roles replace older ones.)
Basic landcycling {1}{W} ({1}{W}, Discard this card: Search your library for a basic land card, reveal it, and put it into your hand, then shuffle.)

[+1]: Remove all counters from target permanent.
[+1]: Each opponent discards a card.
[–2]: Exile target creature or planeswalker card from your graveyard with mana value less than or equal to the number of lands you control. If you do, create a token that's a copy of it.
[–7]: Each opponent gets an emblem with “At the beginning of your upkeep, you lose 7 life unless you sacrifice seven permanents.”

As long as it's your turn, Seto San is a 3/3 Human Warrior creature with indestructible.
[+1]: Up to one target creature you control gains lifelink until end of turn.
[0]: Create a 1/1 white Warrior creature token.
[–X]: Search your library for an Aura or Equipment card with mana value X and put it onto the battlefield, then shuffle.

When Shadowbinder Touka enters or attacks, exile up to one target creature card from a graveyard.
You may play creature cards exiled with Touka.
Sacrifice another creature: Add two mana in any combination of colors. You can't spend this mana to cast spells from your hand. If this mana is spent to cast a creature spell, that creature enters with a finality counter on it.

When Shala Na enters, each player chooses a creature they control, then sacrifices the rest.
[+1]: Up to one target creature you control gains double strike and haste until end of turn.
[–6]: You get an emblem with “Whenever a creature dies, each opponent loses 2 life.”

Pressure {2}{G}{G} (You may cast this spell for its pressure cost if there are seven or more cards in your graveyard.)
Trample, hexproof
Shambling Dreadreef's power and toughness are each equal to the total number of land cards you own on the battlefield and in your graveyard.

You may play Shanty Town from your graveyard as long as seven or more cards are in your graveyard.
Shanty Town enters tapped.
{T}: Add {W} or {B}.
Cycling {1}{W}{B} ({1}{W}{B}, Discard this card: Draw a card.)