msem-instigator

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Scorchland Vandal attacks each combat if able.

Flash
When Scorned Arcanist enters, until end of turn if a creature would enter the battlefield, instead exile that creature and that creature's controller amasses Soldiers X, where X is that creature's mana value. (They put X +1/+1 counters on an Army they control. It's also a Soldier. If they don't control an Army, they create a 0/0 black Soldier Army creature token first.)

When Scorpid Sniper enters, you may have target creature get -1/-1 until end of turn.

Engorge (As this enters, mill three cards, then exile a card from among the milled cards.)
When Scourge of the Deadlands enters, if it engorged a creature card, each other player sacrifices a creature.

When Scrapyard Aberration enters, you may sacrifice another artifact. If you do, target creature gets -2/-2 until end of turn.

Sacrifice Scrapyard Raiders: Target artifact gains indestructible until end of turn.

Trample, prowess

Flying
Whenever you cast a creature spell, if Script Spirit is in your graveyard, you may have it become a copy of that spell until end of turn.

At the beginning of combat on your turn, if you cast both a creature spell and a noncreature spell this turn, untap up to one target land you control. It becomes a 3/1 red Sand creature with haste in addition to its other types until end of turn.

When Scuripi Collector enters, return target artifact, enchantment, or land card from your graveyard to your hand.

{U}: Sea Strider gets +1/-1 until end of turn.
{U}: Sea Strider gets -1/+1 until end of turn.

Haste
Shimmer (Whenever this creature attacks, create a tapped and attacking token that's a copy of it. Exile the token at the beginning of the end step.)

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.

Defender (This creature can't attack.)
Adorned — Secluded Wildborn can attack as though it didn't have defender as long as it's equipped and/or enchanted.

Sabotage — Whenever an opponent or permanent an opponent controls becomes the target of a spell you control, target creature you control can't be blocked this turn.
{B}{B}{B}: Secret Thief gets +3/+0 until end of turn.

{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.

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.)

Whenever you cast your second spell each turn, each opponent loses 1 life and you gain 1 life.

When Seeker's Guardian enters, reveal the top card of your library.

Flying
Whenever Seer of Clear Skies or another creature you control with flying attacks, that creature gets +1/+1 until end of turn.

When Seikatsu Warleader enters, if it's not a token, create a token that's a copy of target creature token you control.

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.

Whenever a Survivor you control dies, you draw a card and you lose 1 life.